Milefortlet 21

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Milefortlet 21 (Swarthy Hill) is part of the Roman coast defences in Cumbria, England. It sits on a low coastal cliff just north of Crosscanonby, with the post‑medieval Allonby Saltpans on the seaward side. It is the only milefortlet that has been fully excavated and is open to the public.

What it was like
- A long‑axis milefortlet with turf ramparts 6 metres wide and timber gates. Internal size: about 14.5 metres by 18 metres.
- The seaward gateway was a 3-metre square opening formed by four posts.
- Inside there was a road (no evidence of a road outside the ramparts).
- To the south‑west of the road were three buildings on sleeper walls, similar in size but with different layouts. The seaward two shared a wall; the third was freestanding. The seaward two contained hearths; the central building had a furnace or oven.
- To the north‑east of the road was a large building, about 18 by 5 metres, divided into four bays. The central bays had hearths, and the outer bays had ovens.
- The fortlet was surrounded by a ditch on all sides except the seaward side, with a causeway at the far end.

Discovery and finds
- In 1968 aerial photos showed cropmarks of the ditch about 64 metres northeast of its predicted site.
- A full excavation in 1990–1991 recovered black burnished and grey ware (including cooking vessels), Samian ware, a bead, a gaming board, a knife, and an object likely an adze. The pottery suggests a single Hadrianic period of occupation.

Towers associated with Milefortlet 21
Milefortlets had two towers located roughly one-third and two-thirds of a Roman mile to the west. The towers for Milefortlet 21 were:
- Tower 21A (Saltpans): Located south of the junction of the B5300 and Crosscanonby Road. Nothing remains above ground today; dismantling was noted just before World War II.
- Tower 21B (Brownrigg North): On the seaward slope of Brown Rigg hill. Only buried remains about two courses high exist; crop marks are visible in aerial photos.

Access
- The usual access point from the milefortlet was closed around 2009–2010.
- You can reach the site via a good, unmarked path starting at a field gate just northeast of the B5300/Crosscanonby Lane junction. Parking is a short distance along Crosscanonby Lane.