The Clashing Gates
A boarding battle between rocks that hate ships.
📜 Session Summary
| Style Kinetic trireme gauntlet — helm checks, boarding fights, and hard navigation choices |
| Win Condition Thread the Symplegades with the ship intact enough to sail and the Titan-kin boarding rite broken |
| Loss Condition The rocks learn the ship's name, crush the route shut, and leave survivors stranded on living stone |
| Setting The Bosphoran strait — fog-wrapped channel between two breathing cliffs that crush ships that linger |
| Atmosphere Ancient elemental dread · the sea as opponent · timing and discipline against blind geological violence |
| Materials Oar-worn pine deck, bronze ram, wax-sealed ropes, fog, black seawater, living stone that exhales |
| Tone Mythic nautical tension — every right decision still leaves something behind |
| Players 6 × Level 10 · 3–3.5 hrs · 3 encounters |
| Key Ally Kyane the Blue Oar (recruit Enc. 1) · Maguffin: Bronze Dove of Phineus |
Description
Captain Philon of the Mist Trireme needs a crew experienced enough to run the Symplegades — the Clashing Gates — because his last crew didn't come back. He is not foolhardy; he simply has no other route. The Titan-kin who inhabit both rocks have learned that boarding parties slow ships down just long enough for the stones to close. The party must run that gauntlet: keep the ship moving, keep the boarders off the helm, and use the Bronze Dove of Phineus at exactly the right moment.
The Symplegades are not merely geographic hazards — they are alive, and the Titan-kin serve them with a ritual of naming: if the rocks learn a ship's name, they can close on it deliberately. Every round spent fighting is a round the chant can progress. Speed is survival; knowing when to fight and when to row is the real skill challenge.
Enc 1: Launch the dove into the channel before the trireme commits. It returns within 1 round bearing information: if it returns with clipped wings (left or right), that rock moves first — the party can set optimal course with Advantage on the first vehicle (water) or Perception check that round. If it returns whole, the rocks are synchronized — both move at the same count.
Enc 2: The dove can be used to identify which Stone Scion is sustaining the anchor chant. Launch it at the Stone Scion's position: DC 14 Perception to read its reaction and confirm the anchor-chant target (automatic if the dove is specifically directed). Without the dove, the party must succeed on a DC 17 Arcana or Insight to identify the right target among the boarders.
Enc 3: The dove's wingbeat at the exact moment of the final gap is the "safe count." Spend it to cancel one rock-clash (the rocks hesitate for a full round, all movement toward each other stops) OR to expose the anchor-chain's weak link (auto-success on the chain-cutting attempt). Once spent, the dove's mechanism winds down permanently — it becomes an ordinary bronze ornament.
Key NPCs
Captain Philon of the Mist Trireme — Quest Giver · Neutral
Philon is a veteran navigator in his late forties: sun-dark, precise in everything except the thing that clearly costs him. He projects complete confidence in planning and loses it without warning in execution — specifically when something goes wrong near the rocks. He hired the party because his own crew is too loyal to refuse him and he knows he'll get them killed if he takes them through the Symplegades again. Secret: he lost his last crew here. He can hear their oars in the fog (DC 15 Perception for anyone nearby to catch him tilting his head toward an empty port side). He will not speak of it — DC 16 Persuasion or DC 14 Insight to get him to acknowledge it, and he gives nothing more. RP hook: If the party asks what happened to the previous crew, he says only: "They were good sailors." DC 14 Insight: he means it as an epitaph. If the party earns a clean run (no ship zone failures), he takes off his pilot ring — worn bronze, sea-smoothed — and presses it into someone's palm before they part ways.
Kyane the Blue Oar — Potential Ally · Neutral
Kyane is the fastest living rower on the Propontis and she knows it — not with arrogance, but with the absolute calm of a person who has settled the question. She's been aboard the Mist Trireme as a hired hand since Enc 1 opens, rowing in silence, watching the party. She will join permanently if they treat her cadence as the authority it is or beat her fairly in a rowing contest (her idea of respect). Secret: she crossed the Symplegades once before, alone, in a fishing skiff. She made it because she rowed for ten straight hours and the rocks couldn't keep up. She has never told this to anyone. RP hook: She responds to honesty about fear ("We don't know if this works") with complete warmth; she responds to bravado with measured silence. DC 14 Persuasion to recruit early by telling her the truth about the odds.
Major Beats
- Approach and the Dove. Philon briefs the party while the fog thickens. The Bronze Dove is launched. Its return tells the party which rock moves first. DC 14 History: the Symplegades haven't let a named ship pass in a generation. DC 16 Arcana: the anchor chant is Titan-kin blood-rite, not sorcery — counter-magic won't work directly.
- Encounter 1 — Dove Before Oars. Navigation challenge: 5 successes before 3 failures (DC 15 vehicles, Athletics, Perception, or Survival). The dove grants Advantage on the first check. Philon's confidence cracks when the rocks answer the trireme's old name. Recruit Kyane by honoring her cadence or besting her in an honest rowing contest. Hard encounter; failure damages a ship zone or starts Enc 2 with boarders already aboard.
- Encounter 2 — Boarders From Both Stones. Titan-kin leap from both cliffs to pin the trireme in place while the gates close. Rock-Grapplers and a Tide-Ogre board from the port side; a Stone Scion sustains the anchor chant from starboard. Non-combat option: beat the Tide-Ogre's cadence (Performance/Athletics DC 16) to stall one bridge. Hard encounter; the dove can identify the Scion.
- Encounter 3 — The Count Between Clashes. The final gap. Seven-count clock. Brontes Gate-Heir boards. The anchor-chain must be cut, the gap run, and Brontes repelled or outwitted. Deadly encounter. Spend the dove to cancel a rock-clash or expose the chain's weak link.
- Resolution. The ship clears the gap. The rocks close behind it with a sound like the world disagreeing with itself. Philon looks back once. If the anchor-chain was cut, the Symplegades will not know this ship's name — for this generation, at least.
Session Rewards
Keepable prizes earned by completing (or excelling at) this session. One character claims each reward unless noted. Full cards are under Reward Cards.
| Reward | Description | Criteria |
|---|---|---|
| Bronze Dove of Phineus | Bronze dove that signals a safe crossing beat and misleads closing hazards. | Time the Symplegades run and keep the dove's timing true through Titan-kin boarders. |
Creature / Enemy List
| Creature | Easy | Med | Hard | Notes |
|---|---|---|---|---|
| Rock-Grappler Raider | — | med | hard | CR 3 · Boarding skirmisher |
| Tide-Ogre Bosun | — | med | hard | CR 5 · Deck breaker |
| Stone Scion of the Gates | — | med | hard | CR 6 · Titan-kin controller |
| Brontes Gate-Heir | — | med | hard | CR 10 · Boss boarder |
| Kyane the Blue Oar | — | 1 | 1 | Recruit Enc. 1 |
The fog off the Bosphoran strait is not weather — it's the rocks breathing. The Mist Trireme's prow cuts through water that smells like stone dust and old salt. Somewhere ahead, the rhythm of an oar is wrong, too slow, and then impossibly regular — and the cliffs above that rhythm are moving. The party has maybe four minutes before the channel closes to a navigable width. Philon at the helm says nothing. He is counting.
Encounter 1 — Dove Before Oars
Overview
Approach the breathing rocks, test the current, and decide whether to trust omen, crew, or speed. The Bronze Dove grants a crucial read on the timing. Navigation challenge: 5 successes before 3 failures. Kyane can be recruited here by honoring her rhythm or matching it honestly.
Challenge Structure
- 5 successes before 3 failures
- DC 15 — vehicles (water), Athletics, Perception, or Survival
- Multiple party members may contribute per round (DM discretion)
Stakes (Failures)
- 1 failure: ship zone takes minor damage; next check at Disadvantage
- 2 failures: Rock-Grapplers board now; Encounter 2 starts with them already aboard
- 3 failures: second ship zone damaged AND Enc 2 starts with full enemy roster already aboard
🗺 Terrain
Trireme deck (90×20 ft, three zones: prow, mid-deck, stern-helm) · fog lane (30 ft visibility) · left and right rock faces (40 ft high, 80 ft apart at start, closing at 5 ft/round after the channel trigger) · three current arrows (advantage on vehicle checks if used; Perception DC 12 to find them)
Mechanics
- Read the current (Perception DC 12 + vehicles DC 14): Identify the fastest lane through the channel. Success grants Advantage on the next two ship checks. Failure wastes an action reading a false current.
- Launch the Bronze Dove (Action, once): Returns in 1 round. Clipped left wing = left rock moves first; clipped right = right; whole bird = synchronized (see DM note block for full payoffs). Grants Advantage on the check immediately following the launch round.
- Kyane's Cadence (DC 14 Persuasion or DC 12 Athletics if matching rhythm honestly): Let Kyane call the stroke. She reduces the DC on the current check by 2 and grants one reroll per encounter thereafter. Failing to consult her makes the next check without the benefit; she doesn't object, she just watches.
- Philon's Knowledge (DC 13 History or Insight): Philon remembers the exact timing from his last run. On success, the party learns the rocks close 5 ft per round, not 10 — and the trireme can make it with 2 fewer successes if it goes now. But Philon goes very still when asked about how he knows this.
- Party finds a wild current that adds 20 ft to the ship's effective movement this encounter only. Encounter 2 begins before boarders reach the gantry — party gets a free round before initiative.
Creature Cards
Captain Philon of the Mist Trireme
Veteran navigator, quest giver
Motivation. He must prove a safe western route before the fleet commits to the passage.
Secret. He once lost a crew here and still hears their oars in the fog.
Hard rule. He will sacrifice cargo before crew, but not the ship's dove unless convinced it saves everyone.
Bronze Dove of Phineus
Clockwork omen, passage key
Appearance: Palm-sized bronze dove with one real white feather in its throat.
Handout. "If it returns with clipped wings, row. If it returns whole, pray faster."
Enc. 1–2. Launch it to scout currents, granting advantage on one vehicle (water) or Perception check.
Enc. 3. Its wingbeat names the safe count; spend it to cancel one rock-clash or expose the Titan-kin anchor.
Kyane the Blue Oar
Medium Humanoid, Neutral · Recruitable Ally · Champion rower and boarding repeller
AC 16 | HP 83 | Speed 30 ft.
Role: Champion rower and boarding repeller
RECRUITMENT (Enc. 1). Let her call cadence during the first crush, or beat her honest in a rowing contest.
Aid. Acts on party initiative when recruited; prefers nonlethal when asked.
Strike. Oar-staff +7 to hit, 14 bludgeoning; grants one reroll on a failed ship check.
Rock-Grappler Raider
Medium Creature · CR 3 · Boarding skirmisher
AC 16 | HP 74 | Speed 30 ft.
Note. Falls inert if shoved into open water between clashes.
Attack. Stone hook +6 to hit, 13 piercing and pulls target 10 ft toward a rail.
The rocks inhale — a sound like all the sea pulling back at once — and then the cliffs are lined with Titan-kin. They don't fall, they step, stone-footed, using handholds that weren't there a moment ago. Boarding bridges hit both rails in the same instant. On the port side an ogre-shaped silhouette the color of wet granite starts singing cadence, and the stroke-count from the rocks is the same as the rowers'. The ship is being forced into rhythm with the walls that will crush it.
Encounter 2 — Boarders From Both Stones
Overview
Titan-kin board from both cliffs simultaneously, using the trireme as an anchor while the Symplegades close. The Stone Scion sustains the anchor chant that teaches the rocks the ship's name. The Tide-Ogre Bosun controls the port boarding bridge. The party must repel boarders, repair oar banks, and break the anchor chant — all while the rocks close 20 ft per initiative-count-20. Hard encounter; the Stone Scion is the priority target once identified.
Creatures (APL10 Hard)
- 3× Rock-Grappler Raider CR 3 (700 XP each)
- 1× Tide-Ogre Bosun CR 5 (1,800 XP)
- 1× Stone Scion of the Gates CR 6 (2,300 XP)
- XP: base ~6,900 × 1.5 multiplier = ~10,350 adj. XP (Hard threshold ≈ 10,800)
Initiative 20 Events (DM chooses one per round)
- Rocks close 20 ft (now at ___ ft apart)
- One ship zone takes 1d6 structural damage (at 3 damage: zone unusable)
- 2 additional Rock-Grapplers board
🗺 Terrain
Main trireme deck (90×20 ft) · port boarding bridge (Tide-Ogre's side) · starboard boarding bridge (Grapplers' side) · stern helm (Philon's position) · mast mid-deck · 2 oar banks (each bank: DC 15 Athletics or tools to repair, 1 Action; Kyane: Bonus Action) · rail hazards (DC 14 Acrobatics after any push-effect or fall from bridge)
Mechanics
- Cadence Contest vs Tide-Ogre (Performance or Athletics DC 16): Challenge the Bosun's rowing cadence. Success: the port boarding bridge stalls for 2 rounds — no Grapplers board from that side and the Tide-Ogre is distracted (Disadvantage on attacks). Kyane can assist, granting Advantage on this check if she's present and directed.
- Identify and Target the Stone Scion (Bronze Dove or DC 17 Arcana/Insight): The anchor chant won't stop while the Scion is alive and sustaining it. The dove auto-identifies which boarder is the Scion (see DM note block). Without the dove, DC 17 Arcana to identify by the resonance in the chant, or DC 15 Perception to notice the rocks respond specifically when this one boarder sings.
- Cut the Port Bridge (DC 15 Athletics or a slashing weapon action): The port boarding bridge is hemp-rope over iron grapples. Cutting it removes the Tide-Ogre's route to the deck (it must make a DC 16 Athletics or fall into the sea between the rocks). Rock-Grapplers must use Acrobatics DC 14 to cross once the bridge is cut — half-speed, Disadvantage on attacks that round.
- Grapplers target the helm and oar banks first. A Grappler reaching the helm forces Philon to defend himself (he uses his Action to fight, not navigate — one fewer success available next Enc 3 check).
- Any Grappler shoved into the water between the rocks is inert — the rocks treat them as part of themselves. They don't resurface.
Creature Cards
Rock-Grappler Raider
Medium Creature · CR 3 · Boarding skirmisher
AC 16 | HP 74 | Speed 30 ft.
Note. Falls inert if shoved into open water between clashes.
Attack. Stone hook +6 to hit, 13 piercing and pulls target 10 ft toward a rail.
Tide-Ogre Bosun
Medium Creature · CR 5 · Deck breaker
AC 15 | HP 118 | Speed 30 ft.
Note. Can be distracted by a shouted cadence contest.
Attack. Anchor maul +8 to hit, 20 bludgeoning and damages a ship zone.
Stone Scion of the Gates
Medium Creature · CR 6 · Titan-kin controller
AC 17 | HP 132 | Speed 30 ft.
Note. Maintains the anchor chant that teaches the rocks the ship's name.
Attack. Shard hymn DC 16 Con, 24 thunder and speed halved.
Kyane the Blue Oar
Medium Humanoid, Neutral · Recruitable Ally · Champion rower and boarding repeller
AC 16 | HP 83 | Speed 30 ft.
Role: Champion rower and boarding repeller
RECRUITMENT (Enc. 1). Let her call cadence during the first crush, or beat her honest in a rowing contest.
Aid. Acts on party initiative when recruited; prefers nonlethal when asked.
Strike. Oar-staff +7 to hit, 14 bludgeoning; grants one reroll on a failed ship check.
The channel is 20 feet wide. The ship is 18 feet wide. The stone is still moving. Brontes Gate-Heir lands on the prow with enough force to crack the ram-timber — not a jump, a step, one foot from the cliff face, the other from the ship, like the rocks lent him the distance. He looks at the helm, then at the party, and says the ship's name. He learned it from the anchor chant. The rocks have known this ship for forty seconds. That is long enough.
Encounter 3 — The Count Between Clashes
Overview
Run the final gap while Brontes boards and the stones try to seal the route. Seven-count clock; the party must assign each action before the count ends. Win conditions: cut the anchor-chain AND clear the gap (removes Brontes's bridge back to the rocks), force Brontes overboard, or bargain with his honor (DC 18 Persuasion — he values being bested with skill, not killed with luck). Deadly encounter; raw XP is ≈16,200 adjusted (Brontes CR 10 + Stone Scion + terrain/clock pressure).
Creatures (APL10 Deadly)
- 1× Brontes Gate-Heir CR 10 (5,900 XP)
- 1× Stone Scion of the Gates CR 6 (2,300 XP) — if not killed in Enc 2
- 2× Rock-Grappler Raider CR 3 (700 XP each) — on stern rail
- XP: base ~9,600 × 1.5–2.0 multiplier = ~14,400–19,200 adj. XP (Deadly ≈ 16,800)
Seven-Count Clock
- Each round: assign Helm (1 PC), Oars (1 PC), Repair if needed (1 PC), Boarder Control (remaining PCs)
- Count 7: rocks touch — ship takes crushing damage (3d10 hull damage; DC 15 Dex save or PC on rail takes 4d6 bludgeoning)
- If all 3 ship zones broken and count reaches 7: ship sinks — see failure consequences
🗺 Terrain
Narrowing channel (closes 5 ft/round) · exposed ram (Brontes's boarding point) · anchor-chain attachment (starboard, DC 15 Athletics or slashing weapon to sever) · sliding deck markers (difficult terrain after each rock-movement) · stern wake (Acrobatics DC 12 to maintain footing at stern after each closure event)
Mechanics
- Cut the anchor-chain (DC 15 Athletics or any slashing weapon; auto-success with Bronze Dove expended): Severs Brontes's connection to the rocks. He must make a DC 16 Athletics check or be pulled off the deck by the chain's recoil. Even if he passes, he can no longer benefit from the rock's movement — his legendary action Advance speed drops to 20 ft.
- Force Brontes overboard (shove or grapple to rail; contested Athletics): The gap is 20 ft of rough water between closing stone walls. Any creature in the water takes 2d10 bludgeoning at the start of each turn from rock pressure. Brontes will not resurface — not because he dies, but because the rocks accept him back.
- Bargain with his honor (DC 18 Persuasion; DC 15 if Kyane speaks and the chain has been cut): Brontes understands competition. If the party can demonstrate that the ship earned the crossing — Kyane's rowing, the dove's precision, the anchor-chain cut — he may grant passage. This does not mean friendship. It means he remembers the right name for what happened.
- Advance (1): Move up to half speed (20 ft, or 40 ft if chain intact).
- Strike (1): One Titan Hammer attack.
- Rock-Call (2): The rocks close an additional 5 ft immediately (outside the normal count). Usable once per encounter.
Creature Cards
Brontes Gate-Heir
Large Creature · CR 10 · Boss boarder · Boss
AC 18 | HP 210 | Speed 40 ft.
Role: Boss boarder
Note. Victory can be cutting his anchor-chain and outrunning him through the clash.
Hard encounter focus. Win condition may be steal, escape, disable, or drive-off — not always kill.
Multiattack / Assault. Titan hammer +9 to hit, 24 bludgeoning plus 10 thunder to the deck.
Advance (1). Move up to half Speed.
Strike (1). One attack from Assault.
Bronze Dove of Phineus
Clockwork omen, passage key
Appearance: Palm-sized bronze dove with one real white feather in its throat.
Handout. "If it returns with clipped wings, row. If it returns whole, pray faster."
Enc. 1–2. Launch it to scout currents, granting advantage on one vehicle (water) or Perception check.
Enc. 3. Its wingbeat names the safe count; spend it to cancel one rock-clash or expose the Titan-kin anchor.
Kyane the Blue Oar
Medium Humanoid, Neutral · Recruitable Ally · Champion rower and boarding repeller
AC 16 | HP 83 | Speed 30 ft.
Role: Champion rower and boarding repeller
RECRUITMENT (Enc. 1). Let her call cadence during the first crush, or beat her honest in a rowing contest.
Aid. Acts on party initiative when recruited; prefers nonlethal when asked.
Strike. Oar-staff +7 to hit, 14 bludgeoning; grants one reroll on a failed ship check.
Stone Scion of the Gates
Medium Creature · CR 6 · Titan-kin controller
AC 17 | HP 132 | Speed 30 ft.
Note. Maintains the anchor chant that teaches the rocks the ship's name.
Attack. Shard hymn DC 16 Con, 24 thunder and speed halved.
⚖️ Difficulty Scaling
As Written ★ — 6 Players, Average Level 10
- Baseline for this guide. Encounter 1–2 are Hard; the final encounter is Deadly for six PCs at average level 10.
- XP budgets (6×L10 thresholds): Hard ≈ 10,800 · Deadly ≈ 16,800. Prefer adding elite pressure, legendary actions, or terrain danger over bloating minion counts past the choke.
Library Standard — 6 Players, Average Level 8
- Dial back: reduce boss HP ~20–25%; cut one legendary action option or recharge breath to 6 only; Favor/track thresholds −1 where present; skill DCs −1; drop one minion wave or −2 CR1–2 creatures from Hard openers.
Easier
- APL 8–9: use the Library Standard (6×L8) box, then shave one more minion wave or remove one recharge ability.
Harder
- APL 11–12: boss HP +20%; +1 legendary; final encounter gains one extra elite or lair pulse; skill DCs +1.
📋 Appendix — Cards
Captain Philon of the Mist Trireme
Veteran navigator, quest giver
Motivation. He must prove a safe western route before the fleet commits to the passage.
Secret. He once lost a crew here and still hears their oars in the fog.
Hard rule. He will sacrifice cargo before crew, but not the ship's dove unless convinced it saves everyone.
Bronze Dove of Phineus
Clockwork omen, passage key
Appearance: Palm-sized bronze dove with one real white feather in its throat.
Handout. "If it returns with clipped wings, row. If it returns whole, pray faster."
Enc. 1–2. Launch it to scout currents, granting advantage on one vehicle (water) or Perception check.
Enc. 3. Its wingbeat names the safe count; spend it to cancel one rock-clash or expose the Titan-kin anchor.
Kyane the Blue Oar
Medium Humanoid, Neutral · Recruitable Ally · Champion rower and boarding repeller
AC 16 | HP 83 | Speed 30 ft.
Role: Champion rower and boarding repeller
RECRUITMENT (Enc. 1). Let her call cadence during the first crush, or beat her honest in a rowing contest.
Aid. Acts on party initiative when recruited; prefers nonlethal when asked.
Strike. Oar-staff +7 to hit, 14 bludgeoning; grants one reroll on a failed ship check.
Rock-Grappler Raider
Medium Creature · CR 3 · Boarding skirmisher
AC 16 | HP 74 | Speed 30 ft.
Note. Falls inert if shoved into open water between clashes.
Attack. Stone hook +6 to hit, 13 piercing and pulls target 10 ft toward a rail.
Tide-Ogre Bosun
Medium Creature · CR 5 · Deck breaker
AC 15 | HP 118 | Speed 30 ft.
Note. Can be distracted by a shouted cadence contest.
Attack. Anchor maul +8 to hit, 20 bludgeoning and damages a ship zone.
Stone Scion of the Gates
Medium Creature · CR 6 · Titan-kin controller
AC 17 | HP 132 | Speed 30 ft.
Note. Maintains the anchor chant that teaches the rocks the ship's name.
Attack. Shard hymn DC 16 Con, 24 thunder and speed halved.
Brontes Gate-Heir
Large Creature · CR 10 · Boss boarder · Boss
AC 18 | HP 210 | Speed 40 ft.
Role: Boss boarder
Note. Victory can be cutting his anchor-chain and outrunning him through the clash.
Hard encounter focus. Win condition may be steal, escape, disable, or drive-off — not always kill.
Multiattack / Assault. Titan hammer +9 to hit, 24 bludgeoning plus 10 thunder to the deck.
Advance (1). Move up to half Speed.
Strike (1). One attack from Assault.
Reward Cards
Post-session keepables. Reward is the first tag. Mechanics below are for ongoing use after this oneshot.
Bronze Dove of Phineus
Reward · Wondrous · 1/Long Rest
Mechanics. Once per long rest, as an action, release the dove: for 1 minute it flies a path you choose within 120 feet, and you and allies within 10 feet of its path ignore difficult terrain from waves, rubble, or shifting stone. Once during that minute, when a trap, closing gate, or environmental hazard would force a Dexterity saving throw, you can use a reaction to grant advantage on that save to creatures of your choice within 30 feet.
Appearance. A palm-sized bronze dove with one real white feather lodged in its throat.
Lore. Phineus's timing-bird, kept after the Clashing Rocks learned to miss one more ship.
Quote. "Fly between the bite — not before, not after." — Phineus
Earn when: Time the Symplegades run and keep the dove's timing true through Titan-kin boarders.