Petra is first referred to in the Novellae Constitutiones by the Eastern Roman emperor Justinian I, dated to 535. It was built to reinforce the Roman authority in the kingdom of Lazica, located on the southeastern shores of the Black Sea and, with the emperor's approval, was named in his honor as Petra Pia Justiniana.[1][2] According to the contemporary historian Procopius, Petra was founded through the efforts of the Roman official John Tzibus, who thereafter exercised tight control of imports into Lazica and controlled local access to luxury commodities and much-needed salt.[3][4] The name of Petra, literally, "rock" in Greek, was a reference to the rocky and precipitous coast where the city was built. Its location between the sea and the cliffs rendered the city inaccessible, except for a narrow and rocky stretch of level ground, which was defended by a defensive wall with two towers.[5]