Between 1705 and 1708, Peter and Paul Fortress was doubled by defensive fortifications to protect its northern side, called the Kronwerk due to its crown shape. Little remains of those old fortifications, the site having been occupied by the old Arsenal building which now houses the Artillery Museum. It was in front of these walls that five Decembrist leaders were hung on 14 July 1826. An obelisk erected where the gallows stood (in front of the east wall of the Arsenal) keeps their memory alive.