diff --git a/crates/model/src/table.rs b/crates/model/src/table.rs
index 2dd46e3b..507b9bd0 100644
--- a/crates/model/src/table.rs
+++ b/crates/model/src/table.rs
@@ -106,39 +106,120 @@ impl Table {
     pub fn height(&self) -> f64 {
         self.rows.iter().map(|r| r.height).sum()
     }
+    /// Insert an empty row before `at`. A merge the new row falls inside grows to cover it.
     pub fn insert_row(&mut self, at: usize) {
         let at = at.min(self.rows.len());
+        let merges = self.merges();
         let h = self.rows.get(at.saturating_sub(1)).map(|r| r.height).unwrap_or(30.0);
         self.rows.insert(at, Row { height: h, cells: (0..self.cols.len()).map(|_| Cell::new("")).collect() });
+        self.set_merges(merges.into_iter().map(|m| m.insert_row(at)));
     }
+    /// Insert an empty column before `at`. A merge the new column falls inside grows to cover it.
     pub fn insert_col(&mut self, at: usize) {
         let at = at.min(self.cols.len());
+        let merges = self.merges();
         let w = self.cols.get(at.saturating_sub(1)).copied().unwrap_or(80.0);
         self.cols.insert(at, w);
         for r in &mut self.rows {
             let i = at.min(r.cells.len());
             r.cells.insert(i, Cell::new(""));
         }
+        self.set_merges(merges.into_iter().map(|m| m.insert_col(at)));
     }
+    /// Delete row `at`. Merges through it shrink; a merge anchored on it moves its anchor (and
+    /// text) to the next row it covers.
     pub fn delete_row(&mut self, at: usize) -> bool {
         if self.rows.len() <= 1 || at >= self.rows.len() {
             return false;
         }
+        let merges = self.merges();
+        for m in &merges {
+            if m.r == at && m.rs > 1 {
+                self.move_anchor((m.r, m.c), (m.r + 1, m.c));
+            }
+        }
         self.rows.remove(at);
+        self.set_merges(merges.into_iter().filter_map(|m| m.delete_row(at)));
         true
     }
+    /// Delete column `at`. Merges through it shrink; a merge anchored on it moves its anchor (and
+    /// text) to the next column it covers.
     pub fn delete_col(&mut self, at: usize) -> bool {
         if self.cols.len() <= 1 || at >= self.cols.len() {
             return false;
         }
+        let merges = self.merges();
+        for m in &merges {
+            if m.c == at && m.gs > 1 {
+                self.move_anchor((m.r, m.c), (m.r, m.c + 1));
+            }
+        }
         self.cols.remove(at);
         for r in &mut self.rows {
             if at < r.cells.len() {
                 r.cells.remove(at);
             }
         }
+        self.set_merges(merges.into_iter().filter_map(|m| m.delete_col(at)));
         true
     }
+    /// The merged areas: every uncovered cell spanning more than one cell, clipped to the grid.
+    fn merges(&self) -> Vec<Merge> {
+        let (nr, nc) = (self.rows.len(), self.cols.len());
+        let mut out = vec![];
+        for (r, row) in self.rows.iter().enumerate() {
+            for (c, cell) in row.cells.iter().enumerate().take(nc) {
+                if cell.is_covered() {
+                    continue;
+                }
+                let rs = (cell.row_span.max(1) as usize).min(nr - r);
+                let gs = (cell.grid_span.max(1) as usize).min(nc - c);
+                if rs > 1 || gs > 1 {
+                    out.push(Merge { r, c, rs, gs });
+                }
+            }
+        }
+        out
+    }
+    /// Rebuild every cell's spans and merge flags from `merges`.
+    fn set_merges(&mut self, merges: impl IntoIterator<Item = Merge>) {
+        for row in &mut self.rows {
+            for cell in &mut row.cells {
+                cell.grid_span = 1;
+                cell.row_span = 1;
+                cell.h_merge = false;
+                cell.v_merge = false;
+            }
+        }
+        for m in merges {
+            if m.rs <= 1 && m.gs <= 1 {
+                continue;
+            }
+            for r in m.r..m.r.saturating_add(m.rs) {
+                for c in m.c..m.c.saturating_add(m.gs) {
+                    if let Some(cell) = self.cell_mut(r, c) {
+                        cell.h_merge = c > m.c;
+                        cell.v_merge = r > m.r;
+                    }
+                }
+            }
+            if let Some(cell) = self.cell_mut(m.r, m.c) {
+                cell.grid_span = u32::try_from(m.gs).unwrap_or(u32::MAX);
+                cell.row_span = u32::try_from(m.rs).unwrap_or(u32::MAX);
+            }
+        }
+    }
+    /// Swap the anchor cell's contents into the cell that takes over as anchor.
+    fn move_anchor(&mut self, from: (usize, usize), to: (usize, usize)) {
+        let Some(a) = self.cell(from.0, from.1).cloned() else { return };
+        let Some(b) = self.cell(to.0, to.1).cloned() else { return };
+        if let Some(x) = self.cell_mut(to.0, to.1) {
+            *x = a;
+        }
+        if let Some(x) = self.cell_mut(from.0, from.1) {
+            *x = b;
+        }
+    }
     /// Merge the rectangle (r0,c0)–(r1,c1) inclusive into its top-left cell.
     pub fn merge(&mut self, r0: usize, c0: usize, r1: usize, c1: usize) -> bool {
         let (r0, r1) = (r0.min(r1), r0.max(r1));
@@ -203,6 +284,56 @@ impl Table {
     }
 }
 
+/// A merged area: anchor (r, c) spanning `rs` rows and `gs` columns.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+struct Merge {
+    r: usize,
+    c: usize,
+    rs: usize,
+    gs: usize,
+}
+
+impl Merge {
+    fn insert_row(self, at: usize) -> Self {
+        if at <= self.r {
+            Merge { r: self.r + 1, ..self }
+        } else if at < self.r + self.rs {
+            Merge { rs: self.rs + 1, ..self }
+        } else {
+            self
+        }
+    }
+    fn insert_col(self, at: usize) -> Self {
+        if at <= self.c {
+            Merge { c: self.c + 1, ..self }
+        } else if at < self.c + self.gs {
+            Merge { gs: self.gs + 1, ..self }
+        } else {
+            self
+        }
+    }
+    fn delete_row(self, at: usize) -> Option<Self> {
+        let m = if at < self.r {
+            Merge { r: self.r - 1, ..self }
+        } else if at < self.r + self.rs {
+            Merge { rs: self.rs - 1, ..self }
+        } else {
+            self
+        };
+        (m.rs > 1 || m.gs > 1).then_some(m)
+    }
+    fn delete_col(self, at: usize) -> Option<Self> {
+        let m = if at < self.c {
+            Merge { c: self.c - 1, ..self }
+        } else if at < self.c + self.gs {
+            Merge { gs: self.gs - 1, ..self }
+        } else {
+            self
+        };
+        (m.rs > 1 || m.gs > 1).then_some(m)
+    }
+}
+
 /// A table style defined in the file (`ppt/tableStyles.xml`), as PowerPoint writes the built-in
 /// styles a deck uses: how each part of a table (whole table, banded rows and columns, first and
 /// last rows and columns, corner cells) is filled, bordered and lettered.
@@ -329,6 +460,97 @@ pub fn table_styles() -> Vec<(String, String)> {
 mod tests {
     use super::*;
 
+    /// Every cell is owned by exactly one anchor (itself or a span over it), and no span leaves the grid.
+    fn assert_topology(t: &Table) {
+        let (nr, nc) = (t.n_rows(), t.n_cols());
+        let mut owner = vec![vec![0u32; nc]; nr];
+        for (r, row) in t.rows.iter().enumerate() {
+            assert_eq!(row.cells.len(), nc);
+            for (c, cell) in row.cells.iter().enumerate() {
+                if cell.is_covered() {
+                    assert_eq!((cell.grid_span, cell.row_span), (1, 1), "covered ({r},{c}) has spans");
+                    continue;
+                }
+                let (rs, gs) = (cell.row_span as usize, cell.grid_span as usize);
+                assert!(r + rs <= nr && c + gs <= nc, "span at ({r},{c}) leaves the grid");
+                for o in owner.iter_mut().skip(r).take(rs) {
+                    for x in o.iter_mut().skip(c).take(gs) {
+                        *x += 1;
+                    }
+                }
+            }
+        }
+        for (r, o) in owner.iter().enumerate() {
+            for (c, n) in o.iter().enumerate() {
+                assert_eq!(*n, 1, "cell ({r},{c}) owned {n} times");
+            }
+        }
+    }
+
+    fn merged() -> Table {
+        // 4x4 with a 2x2 merge at (1,1) holding "M".
+        let mut t = Table::new(4, 4, 400.0, 30.0);
+        if let Some(c) = t.cell_mut(1, 1) {
+            c.text = TextBody::from_text("M");
+        }
+        assert!(t.merge(1, 1, 2, 2));
+        assert_topology(&t);
+        t
+    }
+
+    fn anchor_text(t: &Table, r: usize, c: usize) -> String {
+        t.cell(r, c).unwrap().text.text()
+    }
+
+    #[test]
+    fn row_and_column_edits_keep_merges_consistent() {
+        for at in 0..=4 {
+            let mut t = merged();
+            t.insert_row(at);
+            assert_topology(&t);
+            let mut t = merged();
+            t.insert_col(at);
+            assert_topology(&t);
+        }
+        for at in 0..4 {
+            let mut t = merged();
+            assert!(t.delete_row(at));
+            assert_topology(&t);
+            let mut t = merged();
+            assert!(t.delete_col(at));
+            assert_topology(&t);
+        }
+    }
+
+    #[test]
+    fn inserting_inside_a_merge_grows_it() {
+        let mut t = merged();
+        t.insert_row(2);
+        let a = t.cell(1, 1).unwrap();
+        assert_eq!((a.row_span, a.grid_span), (3, 2));
+        assert!(t.cell(2, 2).unwrap().h_merge && t.cell(2, 2).unwrap().v_merge);
+        t.insert_col(0);
+        assert_eq!(t.cell(1, 2).unwrap().grid_span, 2);
+        assert_eq!(anchor_text(&t, 1, 2), "M");
+        assert_topology(&t);
+    }
+
+    #[test]
+    fn deleting_the_anchor_row_or_column_keeps_the_text() {
+        let mut t = merged();
+        assert!(t.delete_row(1));
+        let a = t.cell(1, 1).unwrap();
+        assert!(!a.is_covered());
+        assert_eq!((a.row_span, a.grid_span), (1, 2));
+        assert_eq!(anchor_text(&t, 1, 1), "M");
+        assert!(t.delete_col(1));
+        let a = t.cell(1, 1).unwrap();
+        assert!(!a.is_covered());
+        assert_eq!((a.row_span, a.grid_span), (1, 1));
+        assert_eq!(anchor_text(&t, 1, 1), "M");
+        assert_topology(&t);
+    }
+
     #[test]
     fn insert_delete_merge_split() {
         let mut t = Table::new(3, 3, 300.0, 30.0);