It takes roughly an hour to drive from Khiva to Biruniy and a further hour to get to Ayaz

The three sites of Ayaz qala: top Ayaz qala 1, middle Ayaz qala 2, and bottom Ayaz qala 3.
Image courtesy of Google Earth.

All three were surveyed in 1937 during the early days of the Khorezm Archaeological Expedition and excavations were carried out at Ayaz qala 3 in 1939. Ayaz qala 1 was investigated in more detail by Yuri Manilov in the late 1960's. 

Ayaz qala 1
Ayaz qala 1 is a fortified refuge that was probably built in the 4th century BC just after Khorezm had gained its independence from Persia. It was one of a chain of fortresses defending the main agricultural settlements of the right bank from possible attack by nomads. The neighbouring forts of Qırq Qız qalacan be seen from its battlements. It is likely that the rulers of Khorezm attempted to maintain friendly relationships with the local tribes and to engage them in trade, thus creating a political buffer zone around the oasis. However there may have been threats from further afield, such as from the warlike Saka roaming along the banks of the lower Syr Darya. Throughout history powerful nomads have shown a propensity to raid rather than trade with their more wealthy settled neighbours.