Ayaz Kala complex consists of three fortresses and is located 24km from Buston village near the salty lake Ayaz-kul. In ancient times and early middle ages the complex protected the northern border of lower Khorezm on the right bank of Amu Darya. The oldest fortress Ayaz Kala I (150x180m) was founded during the Siyavushids in the 4th century BC. It occupies the dominating height on the hilltop (approx. 60 m). The outer contour of the walls is up to 10 meters high and the remains of two-tier arched galleries are preserved till nowadays. The entrance of the fortress was protected by gate fortification building with labyrinth.
In the 3rd century AD the walls of the fortress were additionally forced by semicircular towers over the perimeter. The remains of larger fortress Ayaz Kala III (approx. 5 ha) are located at the bottom of the hill. Inside the fortress, traces of monumental cruciform building were found dating to the 4th–2nd centuries BC. All evidence indicates that the double fortress walls with rectangular towers were built around this building in the 1st–2nd centuries AD.
In the 4th–5th centuries the city rose at that place with the local ruler's palace serving as the center of the city. This palace was a part of Ayaz Kala II complex. Excavation works revealed that the palace had more than 40 premises including decorated grand halls with columns, ceremonial court and temple of fire.
After several hundred years in the 7th–8th centuries the fortress Ayaz Kala II was built above the palace on the hill between Ayaz Kala I and Ayaz Kala III. This fortress probably played the role of a fortified feudal castle and/or citadel of the lower city. The upper parts of the walls of this large high fortress were made as battlements with loopholes for archers. A steep ramp was built towards the entrance gates of Ayaz Kala II.
Desolation of Ayaz Kala was connected with deterioration of water supply but Ayaz Kala I in the 11th–13th centuries still was an important border fortress of Khorezm.