| FOSSE | Ditch dug as a fortification (5) |
| TRENCH | Ditch dug as a fortification |
| MOAT | A ditch dug as a fortification and usually filled with water (4) |
| TRACE | Ground plan of a fortification; an amount of rain too small to be measured; the sum of the diagonal elements of a square matrix; or, a line marked by a recording instrument (5) |
| SCARP | What is the inner wall or slope of a ditch in a fortification? (5) |
| REDAN | Arrow-shaped embankment as part of a fortification (5) |
| CORFE | Village on the Isle of Purbeck, Dorset, housing a fortification famous for its defence by Lady Bankes against a parliamentary army during the English Civil War (5,6) |
| SIEGE | Military action to surround a fortification (5) |
| BULWARK | A wall or structure used as a fortification; rampart (7) |
| EARTHWORK | A large artificial bank of soil, especially one used as a fortification (9) |
| WORK | Energy transfer measured in joules; a creation such as a book, musical composition or piece of embroidery, sewing etc; or, a structure such as a wall, built as part of a fortification (4) |
| GAP | An opening, such as a breach in a fortification's wall; a col; or, a space between a train and a platform (3) |
| BARBICAN | Outer defence of a fortification such as a castle, typically a double tower above a gate or drawbridge (8) |
| TURF | Ditch dug up out of the sward (4) |
| DIKE | Ditch dug initially by aformer president (4) |
| REDOUBT | A temporary defence work built inside a fortification as a last defensive position (7) |
| CASTLEKEEP | Strongest part of a fortification also known as a donjon (6,4) |
| CASTLE | Village on the Isle of Purbeck, Dorset, housing a fortification famous for its defence by Lady Bankes against a parliamentary army during the English Civil War (5,6) |
| PARAPET | Another name for a breastwork wall in a fortification (7) |
| BULWARKHEAD | Leader of a fortification? (This answer is in a trade war with Bee of the dog) |