Vratislav II’s little Romanesque chapel, St. Martin Rotunda, dates from the 11th century. The present look of this rotunda has resulted from numerous repairs. The interior diameter of it is six and a half metres, the apse has a depth of 2.2 metres, and its’ walls are between ninety-five and ninety-seven cm wide. A cannonball is fixed into the wall on top of the portal of the Romanesque Revival to mark the 1757 siege of Prague by the Germans. Initially, the entrance was located on the west side. The rotunda’s got a lantern on its’ roof with a gilded cross on top featuring a sun and a half-moon. This rotunda is presently part of the Roman Catholic Churches.
Recently, archaeologists discovered that it actually contains a secret underground floor that for centuries nobody knew existed. Located in Vysehrad, the rotunda is closed to the public.