http://upload.wikimedia.org/wikipedia/commons/thumb/4/45/Thamudi.jpg/250px-Thamudi.jpg

Mada'in Saleh (Arabic: مدائن صالح, madāʼin Ṣāliḥ), also called Al-Hijr or Hegra (so in Greek and Latin, e.g. by Pliny), is a pre-Islamic archaeological site located in the Al-Ula sector, within the Al Madinah Region of Saudi Arabia. A majority of the vestiges date from the Nabatean kingdom (1st century CE). The site constitutes the kingdom's southernmost and largest settlement after Petra, its capital. Traces of Lihyanite and Roman occupation before and after the Nabatean rule, respectively, can also be found in situ, while accounts from the Qur’an tell of an earlier settlement of the area by the tribe of Thamud in the 3rd millennium BC.

• http://en.wikipedia.org/wiki/Mada'in Saleh
• Hillman 1000 Wonders