In the 11th -12th centuries Merv became the capital of Great Seljuk state and reached the highest prosperity. By the order of Seljuk sultan Melik-shakh the city was surrounded by a fortification and moat. This fortress with the area of over 400 hectares is known as
Sultan - Kala - the Fortress of Sultans. In the northeastern part of Sultan - Kala Shakhriar- ark citadel with palace complexes of sultans, administration buildings and a military barracks - was constructed.
