
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. Along Hadrian`s Wall, milecastles were initiall.....
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http://en.wikipedia.org/wiki/Milecastle

A military base built in connection with Hadrian's Wall. These were (usually) regularly spaced at every Roman mile giving the name. At some points, such as the eastern section of Hadrian's Wall this is uncertain. These fortifications acted as based for small garrisons - though to be part of the larger cohort units.
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http://www.encyclo.co.uk/local/20766

A walled enclosure appearing every Roman mile attached to the south face of Hadrian's Wall with a gate in the north (Wall) and south sides, enclosing ca. 250 - 300 sq. m. A modern term with no Roman equivalent.
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http://www.encyclo.co.uk/visitor-contributions.php
No exact match found.