The cylindrical Powder Tower dates back to the 14th century and is the only survivor of the 18 original towers that punctuated the old city wall. Nine Russian cannonballs from 17th- and 18th-century assaults are embedded in its walls. In the past it has served as a gunpowder store, a prison, a torture chamber and a frat house. It now houses a museum which details the political and military history of Latvia from medieval times to the present day.