Dedan, hidden kingdom - Now known as Al Ula in northern Saudi Arabia, known to the ancient Greeks and Romans as Hijra, Hegra or Egra, the former is about the same distance, about 250 miles north from Medina as Medina is north of Mecca. The location where the extinct tribe of Thamud used to dwell.

In the ruins of the old city there are inscriptions that indicate the Dedanites were preceded by a Minean settlement. The Mineans established a center at this desert oasis in order to protect the incense trade. (Source: Wikipedia)

Refer to: http://en.wikipedia.org/wiki/Dedan