From its origins as a tent encampment, Petra had become an urban center by the end of the first century BC. Typical of ancient Near Eastern settlements, the city grew along the natural contours of the landscape. Even the main street followed the curve of the Wadi Musa, Petra's primary river. At this time the Nabataeans paved the road through the Siq, enabling wheeled vehicles to import locally quarried limestone used in city construction. Many of Petra's main architectural features--including the Treasury, Theater, Temple of the Winged Lions, and Qasr al-Bin-t--appeared during the reign of King Aretas IV (9 BC-AD 40), who was responsible for many of the city's central landmarks.
After the Roman occupation of Nabataea, in AD 106, Petra's development took a new direction. As with most other Roman cities, planners did their best to impose an urban grid on this sprawling settlement. The Romans managed to create one straight road along the central marketplace. Flanked by colonnaded porticos, this linear street clearly served as an architectural imprint of Rome. The Colonnaded Street and Gateway symbolized Rome's political presence in Petra.