The Great Northern War of 1700-1721 spawned many heroes, but only one of them (after almost 200 years) was erected a monument. The name of this brave man is Alexey Stepanovich Kelin. He was a major general of the Russian army and commandant of the legendary Poltava, which resisted the onslaught of the strongest Swedish army in the late 17th and early 18th centuries. Oddly enough, but until recently there was no separate study dedicated to the "valiant commandant" (as he is named in the inscription on the monument). This book, published on the eve of the 300th anniversary of the Poltava battle, largely fills this annoying gap. It also contains a systematic review of all significant fortified cities that played one role or another during the so-called Poltava period of the Great Northern War (October 1708 June 1709).