An Aplan Mortarium, also known as a "Maze of the Dead", was built by the Aplans on their home planet Alfava Metraxis.
Mortaria were large temples with subterranean labyrinths. There were tombs in the walls. The mazes had six levels to represent the ascent of the soul.
During the 47th century, one such Mortarium became infested with Weeping Angels, leading to the downfall of the Aplan civilisation. (TV: The Time of Angels)