The old defensive forts called the Castle of Europe and Castle of Asia (on the northern and southern sides of the strait) are not at the entrance of the Dardanelles but some distance inside. They are the third of the pairs of batteries encountered when entering from the Aegean. This drawing was probably done while the Anglo-French fleet was stationed in Besika Bay, Turkey, anticipating the need to support Turkey against the Russians in the months before the start of the Crimean War. See also PAI0881 and related drawings made at the same time in Mends's 'Trafalgar' sketchbook.