From the World Heritage inscription:
The Incense Route was a network of trade routes extending over two thousand kilometers to facilitate the transport of frankincense and myrrh from the Yemen and Oman in the Arabian Peninsula to the Mediterranean.
The four Nabatean towns of Haluza, Mamshit, Avdat, and Shivta, with their associated fortresses and agricultural landscapes linking them to the Mediterranean, are situated on a segment of this route, in the Negev Desert, in southern Israel. They stretch across a hundred-kilometer section of the desert, from Moa on the Jordanian border in the east to Haluza in the northwest. Together they reflect the hugely profitable trade in Frankincense from south Arabia to the Mediterranean, which flourished from the third century BCE until the second century CE, and the way the harsh desert was colonized for agriculture through the use of highly sophisticated irrigation systems.
Ten of the sites (four towns – Haluza, Mamshit, Avdat and Shivta; four fortresses – Kazra, Nekarot, Makhmal, and Grafon; and the two caravanserai of Moa and Saharonim) lie along, or near to, the main trade route from Petra, capital of the Nabatean Empire in Jordan, to the Mediterranean ports. The town of Mamshit straddles the northern parallel route. Combined, the route and the desert cities along it reflect the prosperity of the Nabatean incense trade over a seven hundred year period, from the 3rd century BCE to the 4th century CE.