Rochester Castle stands on the east bank of the River Medway

River Medway

The River Medway, which is almost entirely in Kent, England, flows for from just inside the West Sussex border to the point where it enters the Thames Estuary....

 in Rochester, Kent, England. The 12th-century keep

Keep

A keep is a type of fortified tower built within castles during the Middle Ages by European nobility. Scholars have debated the scope of the word keep, but usually consider it to refer to large towers in castles that were fortified residences, used as a refuge of last resort should the rest of the...

 or stone tower, which is the castle's most prominent feature, is one of the best preserved in England or France. Located along the River Medway and Watling Street, Rochester was a strategically important royal castle. During the medieval period it helped protect England's south-east coast from invasion.