Kingdom's sites Madain Saleh and Diriyah have already been listed.

Al-Okhdood is the site of an ancient city in the southern part of Saudi Arabia, founded in the 6th or 7th century BC.

The farming community survived possibly until they were annihilated by their Jewish rulers. The buildings are in ruins but still carry inscriptions and pictures. Treasures with silver coins, porcelain pottery and obelisks have also been excavated from several locations in the place.

The campaign for a place on the UNESCO list was launched after a recent article in Al-Bilad Arabic daily stressing the historical and cultural significance of Al-Okhdood and shortly taken up by bloggers. They also appealed to the Saudi Commission for Tourism and Archeology to take necessary steps.

"It is my sincere wish to include this extraordinary historical location in the UNESCO World Heritage list," said Mani Dawus, who wrote “Maria," the first historical novel based on Al-Okhdood city.  Leading Saudi intellectuals who are part of the campaign include Turki Al-Hamad, Muhammad Al-Almaei, Saeed Al-Qahtani, Ebtisam Mutawakkil and Ali Sarar.

Ali Sarar, a historian, said Al-Okhdood was the town where Christians were tortured and burned to death about 1,500 years ago.

The charred bones and thick ashes are still found at some ruins that hint at the story of the horrible religious persecutions dating back to 525 AD.

"The Al-Okhdood sites would require at least 30 years of extensive excavations to unearth its buried secrets," director of archeology in the Najran province Saleh Aal Mereah said, adding that what already had been excavated was only a fragment.

A visitor to the site first sees an encircling wall made of clay and square stones and with guard posts at the top. Inside the wall, the ruins of a huge castle are found among cleared bushes of Arak and Samar trees.

Its walls carry inscriptions, names, and engravings of animals and humans. From the top of the castle the whole city and surrounding regions could be viewed.

The story of the people of Al-Okhdood is mentioned in the chapter “Buruj” of the Holy Qur’an, which refers to a Jewish Himyarite king burning alive thousands of his citizens for converting to Christianity.