An ally of the Roman Empire, the Nabataean kingdom flourished throughout the 1st century. Its power extended far into Arabia along the Red Sea to Yemen, and Petra was a cosmopolitan marketplace, though its commerce was diminished by the rise of the Eastern trade-route from Myos Hormos to Coptos on the Nile. Under the Pax Romana, the Nabataeans lost their warlike and nomadic habits and became a sober, acquisitive, orderly people, wholly intent on trade and agriculture. The kingdom was a bulwark between Rome and the wild hordes of the desert except in the time of Trajan, who reduced Petra and converted the Nabataean client state into the Roman province of Arabia Petraea. By the 3rd century, the Nabataeans had stopped writing in Aramaic and begun writing in Greek instead, and by the 5th century they had converted to Christianity. The new Arab invaders, who soon pressed forward into their seats, found the remnants of the Nabataeans transformed into peasants. Their lands were divided between the new Qahtanite Arab tribal kingdoms of the Byzantine vassals, the Ghassanid Arabs, and the Himyarite vassals, the Kindah Arab Kingdom in North Arabia. The city of Petra was brought to the attention of Westerners by the Swiss explorer Johann Ludwig Burckhardt in 1812.