sentences:  Under the supervision of the colonel of fortifications Baltzar von Dahlheim boulder-filled boats were towed into the very narrow strait, where they were sunk in the shallowest and narrowest parts to render it impassable.A small redoubt with three cannon and 400 men guarded the channel, while four galleys were anchored in the Lännersta sound beyond.Probably in order to apply more pressure on Sweden in the peace negotiations, Apraxin decided to attempt an attack on Stockholm.