In the Roman city planning, a decumanus was an east–west-oriented road in a Roman city or castrum (military camp). The main decumanus was the Decumanus Maximus, or most often simply the Decumanus. In a military camp this connected the Porta Praetoria (closest to the enemy) to the Porta Decumana (away from the enemy).
circa 200 CE
Decumanus Maximus, the colonnaded street, of Petra was the main street with commercial shops on both sides. It stretches from the Main Theater to the Qasa al-Bint. Colonnade street of Petra was built by the Romans after they took control of Petra in 106 CE. That year marked the end of the Nabataean Era. The city then became part of the Roman Empire’s Provincia Arabia. The ancient shops once flanking this avenue are gone or are in ruins.