According to the Eleventh Doctor, the Aplans were a relaxed and cheerful species — a fact he attributed to them having the constant company of a second head. He also described them as prolific builders. Their civilisation left notable landmarks on their home planet of Alfava Metraxis during the Tranolite Period. These included the Aplan Mortaria, sometimes known as Mazes of the Dead. These were large, subterranean labyrinths with tombs in the walls, adorned with statues of the dead. The Mazes had six levels, representing the ascent of the soul in the Aplan religion. The Aplans were fastidious in the recording of their social, cultural and political history.
In the 47th century, a large population of Weeping Angels came to Alfava Metraxis. They quickly caused the collapse of the Aplan civilisation and killed them all. Having hunted the Aplans to extinction, the Angel colony lacked any energy source. Over the centuries, they degraded and went into hibernation. (TV: The Time of Angels)