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In page Kent:

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The sites of Richborough Castle and Dover Castle, along with two strategic sites along Watling Street, were fortified by the Romans and the Dukes of Kent. Other important sites include Canterbury city walls and Rochester Castle.[2] Deal Castle, Walmer Castle, Sandown Castle (whose remains were eroded by the sea in the 1990s) were constructed in late mediaeval times, and HM Dockyard, at Chatham and its surrounding castles and forts—Upnor Castle, Great Lines, and Fort Amherst since then.[citation needed]