thumb|300px|The remains of Milecastle 39 (Castle Nick), near Steel Rigg on [[Hadrian's Wall]]
thumb|300px|The remains of Milecastle 39 (Castle Nick), near Steel Rigg on [[Hadrian's Wall]]
A milecastle was a small fort (fortlet), a rectangular fortification built during the period of the Roman Empire. They were placed at intervals of approximately one Roman mile along several major frontiers, for example Hadrian's Wall in Great Britain (Britannia in the Roman period), hence the name.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).