There are several UNESCO World Heritage Sites in Algeria including Al Qal'a of Beni Hammad, the first capital of the Hammadid empire; Tipasa, a Phoenician and later Roman town; and Djémila and Timgad, both Roman ruins; M'Zab Valley, a limestone valley containing a large urbanized oasis; also the Casbah of Algiers is an important citadel. The only natural World Heritage Sites is the Tassili n'Ajjer, a mountain range.