The Khaznat is carved into the facade of the cliff above al-Siq, and is probably a royal tomb, perhaps that of Aretas IV (r. 9 BCE-40 CE), as indicated by both its location and impressive size. The facade is 24.9 m wide and 38.77 m high to the top of the urn that sits atop the shrine in the center of the upper order. The entrance is flanked by six portico columns of the local "Nabataeanized Corinthian type" (a simplified, blocked-out version of the Corinthian capital), decorated, like the pediment, with floral motifs. The portico is approached by a wide flight of steps and opens into the main tomb chamber, which is undecorated except for the traditional diagonal dressing found throughout Nabataea. The main chamber contains three burial locations, and has two ornate doorways leading to smaller side chambers.

Source:

Hammond, Philip C. "Petra." Grove Art Online. Oxford Art Online. Oxford University Press, accessed January 12, 2015, http://www.oxfordartonline.com/subscriber/article/grove/art/T066760.