#Basic Castle Structure and Terms

Contents

Reference Only. This chapter is a picture — background for imagining a castle as a scene, not data referenced for checks. Converting structures into zones and battlemaps (numbers, Target Numbers, gimmicks) is handled by zone conversion and structures. Up to here is picture; from the next step onward, rules.

#Scent — Before the Gate

After climbing the ridge, the castle stood among the trees.

The first thing visible is an embankment — a slope cut out of earth, the palisade above it, and a watchtower on the corner. The road does not run straight toward the castle gate; it bends once and clings beneath the wall. All the while on the climb, someone had been looking down from above.

A castle is not a list of buildings. A castle is a promise that confines people — a promise written in earth, stone, and gates about whom to keep inside and whom to place outside. This chapter is how to read that promise.

#What Is a Castle — Castle as Promise

A castle has three layered faces.

Military base — grips the neck of roads, rivers, and valleys; stops enemies and gathers allies.
Lord's residence and administrative center — people live there, grain gathers there, orders go out from there.
Symbol of authority — by standing there, it says "whose land is this?"

So a castle is not one building. It is a structure where layered yards — kuruwa (郭) — are stacked concentrically, or like steps along a slope. The inner kuruwa is the core, and the outer kuruwa wrap that core. Even if one layer is breached, the next layer holds again — this logic of layers is the whole castle.

So when imagining a castle, the first thing to count is not the number of towers but the layers of yards.

#Hierarchy of Kuruwa — Honmaru, Ninomaru, Sannomaru

The innermost, highest kuruwa is the honmaru (本丸). The lord's residence and final line of resistance are here, and the symbolic tower, the tenshu (天守), stands above it. It is the hardest place to enter, and the place whose fall ends things.

The second and third kuruwa wrapping the honmaru are the ninomaru (二の丸) and sannomaru (三の丸). Samurai residences, storehouses, troop mustering grounds — and above all, retreat lines. When pressed from outside, defenders fall back one layer inward and stand again.

The farther in, the narrower, higher, and fewer things become. Paths thin out, and people decrease. This hierarchy decides the texture of the fight —

pressing from outside to inside is siege,
falling back inward and enduring is defense,
bypassing layers and entering is Infiltration,
reading collapsed layers is ruin exploration.

All four are ways of reading the same kuruwa hierarchy in order, or in reverse.

#Things That Block — Moats, Earthworks, Stonework, Walls

The outer line of a castle exists to block.

Moat (堀) — a ditch surrounding a kuruwa. There are water moats (水堀) filled with water and dry empty moats (空堀). In mountain castles, dry ditches are more common. Width and depth cut off Approach, force detours, and above all trap attackers below.
Earthwork (土塁) — a bank built by cutting and piling earth. The earth dug from the moat becomes the bank, so moat and earthwork are one body. As the most common and quickest defense line to raise, it is the basic face of Sengoku-period castles.
Stonework / stone wall (石垣) — a sloped wall stacked from stone. It is hard to climb and hard to break. But huge stone walls are closer to a later-period image, so it is better to first imagine Sengoku castles as earth castles.
Wall, fence, palisade (塀·柵·木柵) — light cover on the edges of kuruwa and temporary positions. Quick to raise and quick to fall.

Earthworks are earth, stonework is stone. The single scene of attackers trapped below the bank and looking up is the root of every rule that follows.

#Castle Gates — Otemon and Karametemon

The gate is the one legal hole in the wall.

Otemon (大手門) — the main gate, the front entrance. The largest, most dignified, and best defended. It is where siege pressure gathers.
Karametemon (搦手門) — rear or side gate. A route for supply, Surprise Attack, and escape, and a weakness for Infiltration and collusion.
Masugata (枡形) — an L-shaped trap space inside the gate. Enemies who push through the gate are trapped in a small yard surrounded by walls and attacked from above. A gate is not just a passage; it is a room.

This is why castle gates become the stage most often in this volume — a siege hammers the main gate, Infiltration targets the rear gate, and defense closes every gate.

#High Things — Watchtowers and Tenshu

Watchtower (櫓, yagura) — a structure standing on the corners of kuruwa and atop castle walls. It watches, shoots arrows and teppo, raises signals, stores weapons, and keeps troops waiting. One body does many jobs. Height is sightline, range, and dignity.
Tenshu (天守) — the symbolic tower of the honmaru. In practice it is closer to a place of Command, residence, and authority than a strongpoint for intense fighting. It is a tower built to be seen from afar, not a tower built for fighting to the last inside.

The fact that watchtowers had several jobs becomes hooks for other modes — a sleeping watchtower for infiltrators, and a collapsed watchtower for ruin explorers.

#Things That Keep a Castle Alive — Wells and Storehouses

A castle falls first not to blades, but to thirst and hunger.

Well (井戸) / water source (水の手) — the lifeline of a holdout. Getting water on a mountain is hard, and if the well dries or is fouled, the castle collapses from within.
Storehouse (蔵) — the place for food, gunpowder, and loot. That makes it the first target of fire, explosions, and plunder.

Before blades cross the wall, water and fire often decide the castle's fate first. This is why defense and ruin exploration put these two at the core.

#Roads to the Castle and Below the Castle — Mountain Paths and Castle Town

Mountain path / otemichi (大手道) — a narrow, winding path up to a mountain castle. It bends once, narrows once, and twists again at the entrance (koguchi). By the time you are climbing, you are already fighting.
Castle town (城下町) — the urban area below the castle. It is the stage for supplies, Popular Support, rumors, Infiltration routes, and refugees. A castle stands on top of people — when those people shake, the castle shakes too.

The serious explanation of siting categories for mountain castles, hilltop-flatland castles, and flatland castles, plus Approach routes, is left to terrain and Approach routes. Here, keep only the impression that "a castle has roads and a town below it."

#After Reading — To the Next Chapter

Up to here is picture. If you can now imagine a castle as one scene — layers of kuruwa, pressure below an embankment, a gate as a room, sightlines from height, a drying well, a winding mountain path, and the town beneath it — this chapter has done its job.

For the texture of terrain and Approach routes, go to fc12-01-02.
For turning these structures into actual zones and battlemaps, go to fc12-02-01 and fc12-02-02.

Once again — this chapter is Reference Only. There is not one line of numbers. From the next chapter, the picture becomes rules.

"Before knocking on the castle gate, see whom that gate is keeping inside."