Vlasievskaya Tower is one of only two towers which are all that remain of the 16th-century fortified wall which once surrounded the historical centre. It is named after St Blaise (Vlasi in Russian) and was built in stone between 1658 and 1659. It served as one of the five entrances into the fortress. When it was built an icon known as the Our Lady of the Sign Icon (Znamenskaya Ikona) was painted on the wall and at the end of the 19th century a small chapel dedicated to the icon was built onto the tower. Since then the tower is also sometimes referred to as the Znamenskaya Tower.