Alfava Metraxis was the seventh planet in the Dundra system, in the Garn belt. It was home to the Aplan civilisation until their extinction by Weeping Angels in the mid 47th century. By the 49th century it had been terraformed and colonised by human settlers. The atmosphere boasted a high level of oxygen and a low amounts of toxins. The Alfava Metraxis day was about eleven hours.
The Aplans left landmarks on the planet, including temples, and 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, to represent the ascent of the soul. (TV: The Time of Angels / Flesh and Stone)
The Aplan civilisation came mysteriously to an abrupt end in the mid-47th century. Its downfall was caused by the Weeping Angels, which infested the dark underground Mazes, well hidden amid the numerous statues. Having hunted the Aplans to extinction, the Angel colony lacked any energy source. Over the next four centuries, the energy-deprived Angels began to degrade and lose their form.
In the 49th century, humans terraformed the planet and by the 51st century, six billion humans lived there. By this time, the Angels hidden within the Mortarium were too weak to venture out to attack them so they remained dormant.
During the 51st century, a lone, healthy Angel feigned dormancy and allowed itself to be captured. This ensured its access to the Byzantium, a large starliner with a temporal core. When the ship passed near Alfava Metraxis, the Angel presumably hunted down the crew and crashed it into one of the Mortaria. The Angels in hibernation within the maze began reviving, using the power from the ship to return to full health.
After the crash of the Byzantium, the Eleventh Doctor, Amy Pond and River Song, with a group of twenty clerics, landed on Alfava Metraxis with the intention of tracking down and capturing the Weeping Angel in its vault. The clerics were soon hunted by the reviving Weeping Angels, who outright killed them because they did not need to feed by sending them back in time. Amy also found herself under possession by a Weeping Angel after looking at a recording of the escaped Angel, which peered into her eyes. The Doctor stopped the feeding frenzy by using a crack in time and the failing artificial gravity in the Byzantium to send the Angels tumbling into the crack and out of existence. (TV: The Time of Angels / Flesh and Stone)