Ayaz-kala fortress is located in the north-west of Elikkalin district in the south of Karakalpakstan some 70km from Urgench. It consists of a complex of three fortresses, grouped around a hill in the eastern part of Sultan Uiz Dagh Mountains which were built from the 4th cent. BC to the 7th cent. AD. The three sites linked by road and a series of paths and tracks.
The fortresses were part of a series of forts located at the edge of the Kyzyl-Kum Desert, which provided defense against raids by nomads and the Kipchak-speaking nomadic tribes of the Syr-Darya delta. Ayaz Kala is easily accessible by vehicle from Khiva and Urgench via Biruni and Buston. It is about 70 km from Urgench on a good bitumen road. It is about 32 km from Ayaz Kala to Toprak Kala.
Ayaz Kala I is a fortress dating back to end of the 4th or beginning of the 3rd cent. BC. In this time Khorezm had become independent from Persia. Ayaz Kala I was part of a chain of fortresses protecting the agricultural settlements from attacks invaders from the north (Syrdarya). 
The fortress is situated on the top of a high hill, approx. 120 m, providing wide views over the surrounding plains. The fortress is rectangular in plan with sides 182 and 152 m long. The main axis is oriented from South to North. At the southern end of the axis is a square gateway, which is a typical element of frontier fortresses of Khorezm. The gateway was defended by two rectangular towers that led into a small rectangular chamber. This chamber was overlooked on all sides by high walls from which bowmen could shoot at the enemy in case the first gate was breached.
There is a legend about this fortress, in ancient time Khoresms king ordered his people to build a fortress for protection of the northern borders of his state from raids of desert nomads. He told that the person who could build such a fortress, would have his beautiful daughters hand in marriage. The shepherd Ayaz, who lived on the border of Khoresm, started to build a fortress, but then found out, that the King had broken his word and married his daughter off to another man. The shepherd stopped work on the fortress immediately on finding this out. It is interesting, that as archaeologists found, that it was really unfinished.
Ayaz Kala II is a feudal fortress dating from the 6th to 8th cent. AD. Coins of Khoresmian Kings of Afrigid dynasty, specifically coins of King Bravik, were found here. It was built on the top of a conical hill, about 40 m high, situated south west of Ayaz Kala I. The fortress has the shape of a small oval. It is connected by a steep passage to the open settlement built on level ground to the West of the fortress. You can come inside through the gates from the south-western side, or climb on steep passage, or along the path, enveloping the walls from the northern side. The walls were built from clay press bricks and raised on the base from a mixture of clay and gravel, the upper part of the walls was protected by castellation of archery slits.
During the 6th to 8th cent. AD Khorezm was ruled by the Afrighid dynasty of Khorezmshahs. At this time the "dihqans", a new class of feudal landowners came into existence. They were descendants of the ancient nobility, courtiers or soldiers who had been rewarded for military services. Their agricultural estates were called "rustaq". They lived in "donjons", small square forts surrounded by a defensive wall. An important example us Yakke Parsan which is situated 10 Km south of Ayaz Kala.
Ayaz Kala II was built of rectangular mud bricks on a foundation of "paksha" (cob). The upper parts of the outer walls were crenulated. The building was fortified with low battlements and a row of arrow slits. Ayaz Kala II had a 50 m long sloping man-made staircase on the southern side of the fort. The fort has residential quarters, ceremonial halls with ceilings supported by multiple columns and a fire temple, luxuriously decorated with wall paintings. This building seems to have been the residence of an feudal lord loyal to the Khorezmshah. The building was built in the 4th cent. AD and destroyed by two separate fires. It was in use during the 6th and 7th cent AD as a domestic dwelling. Ayaz Kala II seems the have been the centre of a small rural community and might have been in use until the Mongol invasion in the 13th cent. The best view of the site is from the top of Ayaz Kala I.
Ayaz Kala III is a fortified garrison dating from the 1st to 2nd cent. AD. The monumental building in the north east corner may have been founded in the 5th or 4th cent. BC: The site covers an area of about 5 hectares. The enclosure wall is one of the largest fortresses in Karalpakstan. It has the shape of a parallelogram with sides 260 m and 180 m long. The structure of the external wall is similar to that of Ayaz Kala 1. The external walls are 7.5m wide. The circular watch towers are approx. 8 m in height. The fortress was built with paksha "cob" and masonry (adobe blocks). The entrance to the fortress on the western side consists of an S-Shaped extension of the external wall. The interior of the fortress is largely empty.
The monumental buildings in the north east corner cover an area of 2,400 square meters. The building has 40 rooms divided into 4 groups by 2 central corridors. There are remains of a narrow corridor on three sides of the buildings. The southern and eastern walls have square watch towers Archaeologists believe Ayaz Kala III was used in Kushan times as a garrison and commanders residence and as a refuge for the local farming population and that a small force used Ayaz Kala I as a lookout post. The remains of many farm dwellings and evidence of vineyards were found around walls of the fortress.The best pictures of Ayaz Kala are taken at sunset.
Sources: http://www.centralasia-adventures.com/en/sights/ayaz_kala.html
https://wikitravel.org/en/Ayaz-Kala