In 1235 Shirvanshah Fariburz III had a fortification built on one of the rocky islands of the Baku bay which was subsequently called the Sabael Castle, Shahri Saba, Shahri Nau, the city under water, the caravanserai, the Bail rocks, etc. Wrapped in legends, the castle is completely under water at present and is about 350 meters distant from the shore.

The castle was constructed by the project of the architect Zeynaddin Ibn Abu Rashid Shirvani. The plan of the building has a view of an irregular shaped rectangular of 180 m in length and 40 m in width sharply stretched from the north to the south. This shape coincided with the outlines of the island rising above the sea water on which the foundation of the building is entirely located. The castle was surrounded with the fortress walls of 1,5-2 m in thickness and had 15 towers, three of which were round and 12 - semicircular.

The entire fortress in the upper part is set in a frame with an inscription made of Arabic type. The greater part of the inscription was made in the Persian language – the official language of the period. The general length of the inscription is 400 metres. Each of the stones with an inscription was 70 cm lengthwise and 25-50 cm wide, the thickness reached 15-25 cm. These inscriptions do not have analogues in the entire Near East of the feudal period for their decorative design, the pictures of living creatures, first discovered in the Islamic monuments of the world. The text of the inscription gives the genealogy of the Shirvanshahs’ dynasty Mazyadids. The inscriptions on the stones have not been deciphered up to now. The pictures of different animals perhaps show the years of one or another Shirvanshah. As is generally known, in the medieval period in the Near Eastern countries the years were marked by the names of animals. The pictures of human heads with a crown seem to refer to individual representatives of the Shirvanshahs’ dynasty. Among the proper names one can see on the inscriptions are Mahammad Ibn Yazid, Khalid, Ali, Manuchuhr, Fariburz Afrasiyab, Jamaladdin, etc. One can also see the titles “shah”, “soltan”, the names of cities are also encountered. On one stone one can read Benderi-Baku, that is, the port of Baku. The name of Rashid an-Naggash, that is artist Rashid who had cut out human and animal pictures is also mentioned.

There are different versions about the purpose of the castle. The small width of the exit doors (1,25m) refutes the version that it was a caravanserai, as loaded camels and horses could not pass through them. The researches show that this was a defence sea fortress being at the same time a residence of the Shirvanshahs. The sea fortress on the approaches to Baku was necessary in case of an attack from the seaside. At the end of the XII century the Shirvanshahs had a marine which stood round the fortress. From outside round the walls one can see the stones with an opening to tie the ships.

In the XIII century the Mongols who did not have any fleet, laid siege to the fortress for a long time. Although they did destroy the upper part of the fortress with siege-guns, they could not occupy it.

In 1306 as a result of a strong earthquake in the south of the Caspian and the rise of the sea level the fortress sank into the water. From the beginning of the XIV century and to the beginning of the XVIII century the building was flooded with the Caspian waters. In 1723 in connection with the abatement of the water level in the Caspian the top of the tower appeared from beneath the water. The upper part of the building is completely destroyed, only the lower part of the walls and the towers reaching in some places about 1,5-2 m high is surviving.

The archaeological investigations of the castle were carried out in 1939, 1940, 1946, 1962 and 1969. In the course of the excavations the foundations of 9 habitual premises were discovered, two of them had a hearth. About 700 stones with inscriptions, fragments of earthenware crockery of black and red baking, intact vessels, copper coins of Shirvanshah Kershasb (1203/4-24) and others were lifted from the bottom of the sea. Also were found the fragments of potter’s pipes of different diameters which seemed to be water-pipes. At present part of the stones lifted from the bottom of the sea are displayed in the museum of the Shirvanshahs’ Palace.