diff --git a/crates/citygen/src/generate/arterials.rs b/crates/citygen/src/generate/arterials.rs
index f47226c..39ed42d 100644
--- a/crates/citygen/src/generate/arterials.rs
+++ b/crates/citygen/src/generate/arterials.rs
@@ -130,7 +130,7 @@ impl StageRunner for ArterialsStage {
 #[cfg(test)]
 mod tests {
     use crate::generate::testutil::small;
-    use crate::geom::Rect;
+    use crate::geom::{Grid, Rect};
     use crate::params::WaterMode;
     use crate::pathing::components;
     use crate::tile::Terrain;
@@ -152,7 +152,16 @@ mod tests {
                 .any(|p| st.tiles.get(p).is_some_and(|t| t.terrain == Terrain::Road));
             assert!(near, "district {:?} centre not on road", d.id);
         }
-        let comps = components(st.tiles.size(), |p| st.tiles[p].terrain == Terrain::Road);
+        // The arterial stamps themselves form one connected network.
+        let mut mask = Grid::filled(st.tiles.size(), false);
+        for path in &c.arterials {
+            for p in path {
+                mask.fill_rect(Rect::new(p.x - 1, p.y - 1, 4, 4), true);
+            }
+        }
+        let comps = components(st.tiles.size(), |p| {
+            mask[p] && matches!(st.tiles[p].terrain, Terrain::Road | Terrain::Bridge)
+        });
         assert_eq!(comps.len(), 1);
     }
 
diff --git a/crates/citygen/src/generate/mod.rs b/crates/citygen/src/generate/mod.rs
index 8c43858..a9b72fe 100644
--- a/crates/citygen/src/generate/mod.rs
+++ b/crates/citygen/src/generate/mod.rs
@@ -2,6 +2,7 @@
 
 pub mod arterials;
 pub mod districts;
+pub mod streets;
 pub mod terrain;
 
 use crate::flavor::FlavorPack;
@@ -225,6 +226,7 @@ pub(crate) fn runner_for(stage: Stage) -> Box<dyn StageRunner> {
         Stage::Terrain => Box::new(terrain::TerrainStage::default()),
         Stage::Districts => Box::new(districts::DistrictsStage::default()),
         Stage::Arterials => Box::new(arterials::ArterialsStage::default()),
+        Stage::Streets => Box::new(streets::StreetsStage::default()),
         _ => Box::new(NoopStage),
     }
 }
diff --git a/crates/citygen/src/generate/streets.rs b/crates/citygen/src/generate/streets.rs
new file mode 100644
index 0000000..6de03ae
--- /dev/null
+++ b/crates/citygen/src/generate/streets.rs
@@ -0,0 +1,495 @@
+//! Stage 4: per-district street subdivision and block extraction.
+
+use super::{Block, GenCtx, Stage, StageRunner, StepOut};
+use crate::geom::{Pos, Rect};
+use crate::ids::DistrictId;
+use crate::params::GenError;
+use crate::rng::chance;
+use crate::theme::StreetStyle;
+use crate::tile::{Feature, Terrain};
+use crate::world::StratumKind;
+use rand::Rng;
+use rand_chacha::ChaCha8Rng;
+
+#[derive(Default)]
+pub(crate) struct StreetsStage {
+    next: usize,
+    rng: Option<ChaCha8Rng>,
+}
+
+/// Paints `terrain` at `p` only on untouched land of this district.
+fn paint_cell(ctx: &mut GenCtx, p: Pos, d: DistrictId, terrain: Terrain) {
+    if ctx.is_land(p)
+        && ctx.in_district(p, d)
+        && ctx.terrain(StratumKind::Street, p) == Terrain::Void
+    {
+        ctx.set_terrain(StratumKind::Street, p, terrain);
+        if terrain != Terrain::Sidewalk {
+            ctx.scratch.road.set(p, true);
+        }
+    }
+}
+
+/// A straight street segment to paint.
+#[derive(Clone, Copy)]
+struct Line {
+    terrain: Terrain,
+    width: i32,
+    sidewalk: bool,
+}
+
+impl Line {
+    const fn road(width: i32, sidewalk: bool) -> Self {
+        Line {
+            terrain: Terrain::Road,
+            width,
+            sidewalk,
+        }
+    }
+    const ALLEY: Line = Line {
+        terrain: Terrain::Alley,
+        width: 1,
+        sidewalk: false,
+    };
+}
+
+/// A vertical street starting at column `x`, rows `y0..y1`.
+fn paint_vline(ctx: &mut GenCtx, x: i32, y0: i32, y1: i32, line: Line, d: DistrictId) {
+    for y in y0..y1 {
+        for dx in 0..line.width {
+            paint_cell(ctx, Pos::new(x + dx, y), d, line.terrain);
+        }
+        if line.sidewalk {
+            paint_cell(ctx, Pos::new(x - 1, y), d, Terrain::Sidewalk);
+            paint_cell(ctx, Pos::new(x + line.width, y), d, Terrain::Sidewalk);
+        }
+    }
+}
+
+/// A horizontal street starting at row `y`, columns `x0..x1`.
+fn paint_hline(ctx: &mut GenCtx, y: i32, x0: i32, x1: i32, line: Line, d: DistrictId) {
+    for x in x0..x1 {
+        for dy in 0..line.width {
+            paint_cell(ctx, Pos::new(x, y + dy), d, line.terrain);
+        }
+        if line.sidewalk {
+            paint_cell(ctx, Pos::new(x, y - 1), d, Terrain::Sidewalk);
+            paint_cell(ctx, Pos::new(x, y + line.width), d, Terrain::Sidewalk);
+        }
+    }
+}
+
+/// Positions of parallel street lines across `[lo, hi)` with the given pitch and a random offset.
+fn line_positions(rng: &mut ChaCha8Rng, lo: i32, hi: i32, pitch: i32) -> Vec<i32> {
+    let offset = rng.random_range(0..pitch.max(1));
+    let mut out = Vec::new();
+    let mut x = lo + offset;
+    while x < hi {
+        out.push(x);
+        x += pitch;
+    }
+    out
+}
+
+/// Blocks between consecutive line positions; `gap` is the street width plus sidewalks.
+fn cells_between(lines: &[i32], lo: i32, hi: i32, gap: i32, pad: i32) -> Vec<(i32, i32)> {
+    let mut edges = vec![lo - gap];
+    edges.extend_from_slice(lines);
+    edges.push(hi);
+    edges
+        .windows(2)
+        .map(|w| (w[0] + gap + pad, w[1] - pad))
+        .filter(|(a, b)| b > a)
+        .collect()
+}
+
+struct Carver<'a> {
+    ctx: &'a mut GenCtx,
+    rng: &'a mut ChaCha8Rng,
+    d: DistrictId,
+    bounds: Rect,
+    candidates: Vec<Rect>,
+}
+
+impl Carver<'_> {
+    fn grid(&mut self, bw: i32, bh: i32, sw: i32, sidewalk: bool) -> (Vec<i32>, Vec<i32>) {
+        let pad = if sidewalk { 1 } else { 0 };
+        let b = self.bounds;
+        let xs = line_positions(self.rng, b.x, b.right(), bw + sw + 2 * pad);
+        let ys = line_positions(self.rng, b.y, b.bottom(), bh + sw + 2 * pad);
+        for x in &xs {
+            paint_vline(
+                self.ctx,
+                *x,
+                b.y,
+                b.bottom(),
+                Line::road(sw, sidewalk),
+                self.d,
+            );
+        }
+        for y in &ys {
+            paint_hline(
+                self.ctx,
+                *y,
+                b.x,
+                b.right(),
+                Line::road(sw, sidewalk),
+                self.d,
+            );
+        }
+        for (x0, x1) in cells_between(&xs, b.x, b.right(), sw, pad) {
+            for (y0, y1) in cells_between(&ys, b.y, b.bottom(), sw, pad) {
+                self.candidates.push(Rect::new(x0, y0, x1 - x0, y1 - y0));
+            }
+        }
+        (xs, ys)
+    }
+
+    fn organic(&mut self, rect: Rect, max_w: i32, max_h: i32, depth: u8) {
+        const MIN_W: i32 = 8;
+        const MIN_H: i32 = 6;
+        let split_w = rect.w > max_w && rect.w > 2 * MIN_W;
+        let split_h = rect.h > max_h && rect.h > 2 * MIN_H;
+        if depth == 0 || (!split_w && !split_h) {
+            self.candidates.push(rect);
+            return;
+        }
+        let vertical = if split_w && split_h {
+            rect.w >= rect.h
+        } else {
+            split_w
+        };
+        let jitter = self.rng.random_range(0.35..0.65);
+        if vertical {
+            let s = (rect.x + (rect.w as f32 * jitter) as i32)
+                .clamp(rect.x + MIN_W, rect.right() - MIN_W - 1);
+            paint_vline(self.ctx, s, rect.y, rect.bottom(), Line::ALLEY, self.d);
+            self.organic(
+                Rect::new(rect.x, rect.y, s - rect.x, rect.h),
+                max_w,
+                max_h,
+                depth - 1,
+            );
+            self.organic(
+                Rect::new(s + 1, rect.y, rect.right() - s - 1, rect.h),
+                max_w,
+                max_h,
+                depth - 1,
+            );
+        } else {
+            let s = (rect.y + (rect.h as f32 * jitter) as i32)
+                .clamp(rect.y + MIN_H, rect.bottom() - MIN_H - 1);
+            paint_hline(self.ctx, s, rect.x, rect.right(), Line::ALLEY, self.d);
+            self.organic(
+                Rect::new(rect.x, rect.y, rect.w, s - rect.y),
+                max_w,
+                max_h,
+                depth - 1,
+            );
+            self.organic(
+                Rect::new(rect.x, s + 1, rect.w, rect.bottom() - s - 1),
+                max_w,
+                max_h,
+                depth - 1,
+            );
+        }
+    }
+
+    fn rows(&mut self, row_h: i32, access_pitch: i32) {
+        let b = self.bounds;
+        let ys = line_positions(self.rng, b.y, b.bottom(), row_h + 4);
+        let xs = line_positions(self.rng, b.x, b.right(), access_pitch);
+        for y in &ys {
+            paint_hline(self.ctx, *y, b.x, b.right(), Line::road(2, true), self.d);
+        }
+        for x in &xs {
+            paint_vline(self.ctx, *x, b.y, b.bottom(), Line::road(2, true), self.d);
+        }
+        for (x0, x1) in cells_between(&xs, b.x, b.right(), 2, 1) {
+            for (y0, y1) in cells_between(&ys, b.y, b.bottom(), 2, 1) {
+                self.candidates.push(Rect::new(x0, y0, x1 - x0, y1 - y0));
+            }
+        }
+    }
+
+    fn shattered(&mut self) {
+        let (xs, ys) = self.grid(16, 10, 2, false);
+        let b = self.bounds;
+        // Cut 30% of the vertical segments between consecutive horizontal streets.
+        let mut ybounds = vec![b.y - 2];
+        ybounds.extend_from_slice(&ys);
+        ybounds.push(b.bottom());
+        for x in &xs {
+            for w in ybounds.windows(2) {
+                if !chance(self.rng, 0.3) {
+                    continue;
+                }
+                let (y0, y1) = (w[0] + 2, w[1]);
+                if y1 - y0 < 3 {
+                    continue;
+                }
+                let mut cut = Vec::new();
+                for y in y0..y1 {
+                    for dx in 0..2 {
+                        let p = Pos::new(x + dx, y);
+                        let mine = self.ctx.in_district(p, self.d)
+                            && self.ctx.terrain(StratumKind::Street, p) == Terrain::Road
+                            && !self.ctx.scratch.arterial[p];
+                        if mine {
+                            self.ctx.set_terrain(StratumKind::Street, p, Terrain::Alley);
+                            cut.push(p);
+                        }
+                    }
+                }
+                if let (Some(first), Some(last)) = (cut.first().copied(), cut.last().copied()) {
+                    self.ctx
+                        .set_feature(StratumKind::Street, first, Some(Feature::Barrier));
+                    self.ctx
+                        .set_feature(StratumKind::Street, last, Some(Feature::Barrier));
+                }
+            }
+        }
+    }
+
+    fn strip(&mut self) {
+        let b = self.bounds;
+        let center = self.ctx.city.district(self.d).center;
+        let horizontal = b.w >= b.h;
+        if horizontal {
+            let y = center.y - 1;
+            paint_hline(self.ctx, y, b.x, b.right(), Line::road(3, true), self.d);
+            let xs = line_positions(self.rng, b.x, b.right(), 10);
+            for x in &xs {
+                paint_vline(self.ctx, *x, b.y, b.bottom(), Line::ALLEY, self.d);
+            }
+            for (x0, x1) in cells_between(&xs, b.x, b.right(), 1, 0) {
+                self.candidates
+                    .push(Rect::new(x0, b.y, x1 - x0, y - 1 - b.y));
+                self.candidates
+                    .push(Rect::new(x0, y + 4, x1 - x0, b.bottom() - (y + 4)));
+            }
+        } else {
+            let x = center.x - 1;
+            paint_vline(self.ctx, x, b.y, b.bottom(), Line::road(3, true), self.d);
+            let ys = line_positions(self.rng, b.y, b.bottom(), 10);
+            for y in &ys {
+                paint_hline(self.ctx, *y, b.x, b.right(), Line::ALLEY, self.d);
+            }
+            for (y0, y1) in cells_between(&ys, b.y, b.bottom(), 1, 0) {
+                self.candidates
+                    .push(Rect::new(b.x, y0, x - 1 - b.x, y1 - y0));
+                self.candidates
+                    .push(Rect::new(x + 4, y0, b.right() - (x + 4), y1 - y0));
+            }
+        }
+    }
+
+    /// Shrinks a candidate until every cell is untouched land of this district.
+    fn fit_block(&self, mut r: Rect) -> Option<Rect> {
+        let bad = |ctx: &GenCtx, p: Pos| {
+            !ctx.is_land(p)
+                || !ctx.in_district(p, self.d)
+                || ctx.terrain(StratumKind::Street, p) != Terrain::Void
+        };
+        for _ in 0..12 {
+            if r.w < 5 || r.h < 4 {
+                return None;
+            }
+            let top = (r.x..r.right())
+                .filter(|x| bad(self.ctx, Pos::new(*x, r.y)))
+                .count();
+            let bottom = (r.x..r.right())
+                .filter(|x| bad(self.ctx, Pos::new(*x, r.bottom() - 1)))
+                .count();
+            let left = (r.y..r.bottom())
+                .filter(|y| bad(self.ctx, Pos::new(r.x, *y)))
+                .count();
+            let right = (r.y..r.bottom())
+                .filter(|y| bad(self.ctx, Pos::new(r.right() - 1, *y)))
+                .count();
+            if top + bottom + left + right == 0 {
+                let interior_bad = r.inset(1).iter().any(|p| bad(self.ctx, p));
+                if !interior_bad {
+                    return Some(r);
+                }
+                // An interior obstacle (arterial crossing); shrink the side nearest to it.
+                let p = r
+                    .inset(1)
+                    .iter()
+                    .find(|p| bad(self.ctx, *p))
+                    .expect("interior_bad");
+                if (p.x - r.x) * r.h < (p.y - r.y) * r.w {
+                    r = Rect::new(p.x + 1, r.y, r.right() - p.x - 1, r.h);
+                } else {
+                    r = Rect::new(r.x, p.y + 1, r.w, r.bottom() - p.y - 1);
+                }
+                continue;
+            }
+            let top_f = top as f32 / r.w as f32;
+            let bottom_f = bottom as f32 / r.w as f32;
+            let left_f = left as f32 / r.h as f32;
+            let right_f = right as f32 / r.h as f32;
+            let max = top_f.max(bottom_f).max(left_f).max(right_f);
+            if max == top_f {
+                r = Rect::new(r.x, r.y + 1, r.w, r.h - 1);
+            } else if max == bottom_f {
+                r = Rect::new(r.x, r.y, r.w, r.h - 1);
+            } else if max == left_f {
+                r = Rect::new(r.x + 1, r.y, r.w - 1, r.h);
+            } else {
+                r = Rect::new(r.x, r.y, r.w - 1, r.h);
+            }
+        }
+        None
+    }
+}
+
+impl StreetsStage {
+    fn carve_district(&mut self, ctx: &mut GenCtx, idx: usize) {
+        let district = ctx.city.districts[idx].clone();
+        let spec = district.theme.spec();
+        let rng = self.rng.as_mut().expect("begin sets rng");
+        let mut carver = Carver {
+            ctx,
+            rng,
+            d: district.id,
+            bounds: district.bounds,
+            candidates: Vec::new(),
+        };
+        match spec.street_style {
+            StreetStyle::Grid => {
+                carver.grid(spec.block.0, spec.block.1, 2, true);
+            }
+            StreetStyle::Superblock => {
+                carver.grid(spec.block.0, spec.block.1, 2, true);
+            }
+            StreetStyle::Organic => {
+                let (max_w, max_h) = (spec.block.0 * 3 / 2, spec.block.1 * 3 / 2);
+                let b = carver.bounds;
+                carver.organic(b, max_w, max_h, 7);
+            }
+            StreetStyle::Rows => carver.rows(14, 24),
+            StreetStyle::Shattered => carver.shattered(),
+            StreetStyle::Strip => carver.strip(),
+        }
+        let candidates = std::mem::take(&mut carver.candidates);
+        let mut blocks: Vec<Block> = Vec::new();
+        for c in candidates {
+            let Some(c) = c.clamp_to(carver.bounds) else {
+                continue;
+            };
+            if let Some(fitted) = carver.fit_block(c)
+                && blocks.iter().all(|b| !b.rect.intersects(fitted))
+            {
+                blocks.push(Block {
+                    rect: fitted,
+                    district: district.id,
+                });
+            }
+        }
+        carver.ctx.scratch.blocks.extend(blocks);
+    }
+}
+
+impl StageRunner for StreetsStage {
+    fn begin(&mut self, ctx: &mut GenCtx) -> Result<(), GenError> {
+        self.rng = Some(ctx.rng(Stage::Streets));
+        self.next = 0;
+        ctx.scratch.blocks.clear();
+        Ok(())
+    }
+
+    fn step(&mut self, ctx: &mut GenCtx) -> Result<StepOut, GenError> {
+        let n = ctx.city.districts.len();
+        if self.next >= n {
+            return Ok(StepOut::Finished);
+        }
+        self.carve_district(ctx, self.next);
+        self.next += 1;
+        Ok(StepOut::Continue(self.next as f32 / n as f32))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::generate::testutil::small;
+    use crate::generate::{Generator, Stage};
+    use crate::params::{GenParams, SizePreset, WaterMode};
+    use crate::pathing::components;
+    use crate::tile::{Feature, Terrain};
+    use crate::world::{StratumKind, Theme};
+
+    #[test]
+    fn blocks_are_inside_districts_and_off_roads() {
+        let ctx = Generator::run_until(
+            GenParams {
+                seed: 31,
+                water: WaterMode::Bay,
+                districts: 7,
+                size: SizePreset::Custom { w: 120, h: 60 },
+                ..Default::default()
+            },
+            Stage::Streets,
+        );
+        let st = ctx.city.stratum(StratumKind::Street).unwrap();
+        let blocks = &ctx.scratch.blocks;
+        assert!(blocks.len() > 20, "only {} blocks", blocks.len());
+        for b in blocks {
+            assert!(b.rect.w >= 5 && b.rect.h >= 4, "{:?}", b.rect);
+            for p in b.rect.iter() {
+                let t = &st.tiles[p];
+                assert_eq!(t.district, Some(b.district), "{p:?} in {:?}", b.rect);
+                assert!(
+                    !matches!(
+                        t.terrain,
+                        Terrain::Road | Terrain::Alley | Terrain::Water | Terrain::Sidewalk
+                    ),
+                    "{p:?} is {:?}",
+                    t.terrain
+                );
+            }
+        }
+        for (i, a) in blocks.iter().enumerate() {
+            for b in &blocks[i + 1..] {
+                assert!(
+                    !a.rect.intersects(b.rect),
+                    "{:?} overlaps {:?}",
+                    a.rect,
+                    b.rect
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn street_network_is_connected_per_street_level() {
+        let c = small(31, WaterMode::None, 6);
+        let st = c.stratum(StratumKind::Street).unwrap();
+        let comps = components(st.tiles.size(), |p| {
+            matches!(
+                st.tiles[p].terrain,
+                Terrain::Road | Terrain::Alley | Terrain::Sidewalk
+            )
+        });
+        let total: usize = comps.iter().map(|c| c.len()).sum();
+        let share = comps[0].len() as f32 / total as f32;
+        assert!(share > 0.97, "main street component only {share}");
+    }
+
+    #[test]
+    fn combat_zone_has_barriers_and_grid_has_none() {
+        let c = small(31, WaterMode::None, 7);
+        let st = c.stratum(StratumKind::Street).unwrap();
+        let count = |theme: Theme| {
+            st.tiles
+                .iter()
+                .filter(|(_, t)| {
+                    t.feature == Some(Feature::Barrier)
+                        && t.district.map(|d| c.district(d).theme) == Some(theme)
+                })
+                .count()
+        };
+        assert!(count(Theme::CombatZone) > 0);
+        assert_eq!(count(Theme::CorpCore), 0);
+    }
+}