This text is a fragment of a guidebook to Istanbul: "Byzantine Secrets of Istanbul".

Many travellers visiting Istanbul are aware of the ancient Basilica Cistern, an underground water reservoir located near Hagia Sophia. The huge capital of the Eastern Roman Empire - Constantinople - needed a lot of water, so it had plenty of such cisterns and many of them have survived to our times. Moreover, in addition to underground reservoirs, such as the so-called Theodosius Cistern, there were huge open-air cisterns in the city, and Aspar Cistern is one of them.

We have already met Aspar, who gave his name to the cistern, on the occasion of the story of Column of Marcian. Aspar was a kind of politician who remained in the shadows and had a huge impact on the choice of the Eastern Roman emperors. Flavius ​​Ardaburius Aspar was the son of Flavius ​​Ardabur of the Alan tribe, and his name meant Horse Rider. Both father and son were Arians by religion, but despite official documents forbidding Arians from holding offices in the empire, both rose to high positions within the state. On the other hand, as an Arian, Aspar could not aspire to the highest dignity - of an emperor - and instead placed his favourites on the Eastern Roman throne, first Marcian and then Leo.

Aspar played an important role in the expedition organized by his father in 424 against the usurper to the Western throne, Joannes of Ravenna. Joannes lost the fight for the throne, betrayed by the officers who let Aspar's troops into Ravenna. Empress Galla Placidia and her son Valentinian III were placed on the throne. Aspar also participated in peace negotiations with Genseric, king of the Vandals, who travelled with his tribe to Africa, where he created a new Germanic state. After the African campaign, in 434, Aspar was awarded the title of consul.

Emperor Leo I, who reigned from 457, tried to free himself from Aspar's control and lead an independent policy, relying on Isaurian troops led by Tarasikodiss, who changed his name to Zeno. During the struggle for influence at the imperial court between Zeno and Aspar, Aspar persuaded the emperor to appoint his son, Patricius, as Caesar and give him in marriage his daughter Leontia. At the news of these events, the people of Constantinople rebelled and gathered at the Hippodrome, under the influence of the Sleepless Monks, known to pray twenty-four hours a day. Emperor Leo I and Aspar had to make a promise that Patricius would abandon Arianism before marrying Leontia.

However, the following year, Emperor Leo finally dealt with Aspar, thanks to an agreement with the Isaurians. Hosting him and his sons at the palace, he ordered them to be killed on the pretext of conspiracy. Aspar and his older son Ardabur died, but Patricius most likely managed to escape. After this episode, Patricius disappears from the sources, but it is known that his marriage with Leontia was annulled.

Aspar's death caused a riot of his followers in Constantinople. They were led by Comes Ostrys, a companion of Aspar, who led the troops of the Goths. The Goths began to riot in Constantinople and Ostrys attacked the palace with a Gothic army, but was defeated. Undeterred, Ostrys withdrew to Thrace where he began to plunder the estates. His devotion to Aspar was recorded in a saying, "No dead man had a better friend than Ostrys." Aspar's murder also caused the Goths stationed in Thrace under Theoderic Strabo to attack the empire. Strabo was the brother of Aspar's wife and was also related to Ostrys, possibly even as his son. These events initiated the years of war between the Romans and their Gothic allies in Thrace. These clashes continued until 473, but Aspar's death marked the end of Germanic influence in the politics of the Eastern Roman Empire.

The most important material memento of Aspar is the water reservoir bearing his name, Aspar Cistern. It is located on the eastern slope of the fifth hill of Constantinople, over the waters of the Golden Horn. The cistern is located in the district of Çukurbostan, which owes its name to the Ottoman term for the cistern - Sultan Selim Çukurbostanı, or Sultan Selim's Sunken Garden. Another name for this reservoir is Çarşamba Çukurbostanı, meaning the Wednesday Sunken Garden.

Aspar Cistern is one of the three preserved open reservoirs located in the western part of the city, on the fifth, sixth, and seventh hills, between the older defensive walls built by Constantine, now non-existent, and the newer fortifications from the time of Theodosius II. The other two reservoirs in this area are Aetius Cistern and the largest of them - Saint Mocius Cistern. Outside the city walls, in the suburb of Hebdomon (now Bakirköy), there was another such cistern, now known as Fildamı Sarnıcı, or Elephant Stables Cistern.

All three cisterns within the city were built in the 5th century, when the development of Constantinople caused a sharp increase in water demand. Open reservoirs collected spring water, brought from outside the city, from the territory of Thrace by a water conveyance system, the most famous part of which is the Valens Aqueduct. Aspar and Aetius cisterns lay along this system, but the origins of the water in Mocius Cistern, located further to the south, is uncertain. The reservoirs were constructed using the same construction technique, called opus listatum, of alternating rows of bricks and stones, typical of the city's development during this period.

Aspar Cistern was built in 459 in the fourteenth region of Constantinople in the area then known as Petrion. Its construction is evidenced by an entry in the Chronicon Paschale (the Paschal or Easter Chronicle). This anonymous Byzantine chronicle was written between 631 and 641 and described the events from the beginning of the world.

The cistern was built on a square plan with a side length of 152 meters. In its case, the lines of bricks are 50 cm high, and the lines of stones are 1.2 meters high. The wall surrounding the tank is over five meters thick and between 10 and 11 meters high.

There is a known illustration of Aspar Cistern placed in the work called Geodesia by an anonymous author referred to conventionally as Hero of Byzantium, created in the mid-10th century. It shows this cistern filled to the brim with water, but most likely it was a trick to emphasize its importance as a reservoir for the city. In practice, modern researchers estimate that the cistern could not be filled above a height of 7.5 to 9.5 meters due to the water pressure on its walls. Such estimates show that Aspar Cistern could contain from 231 to 254 thousand cubic meters of water.

The issue of controlling the pressure of water flowing from open cisterns has not been fully resolved. Both Aspar and Aetius Cisterns are surrounded by small covered cisterns that may have played a role in regulating the water pressure. Moreover, in the 10th century, a cylindrical tower was added to Aspar Cistern's northern corner, which may have been used to regulate the pressure.

Since the area between the two lines of the fortifications of Constantinople was used for agricultural purposes, the water the open cisterns collected was probably used for irrigation. These crops played a key role in feeding the people of Constantinople, especially in the event of the siege of the city. In the period from 626 to 765, when the Valens water supply system was destroyed, open cisterns were not used. Most likely, they were reused later, as evidenced by the above-mentioned illustration from Geodesia.

Around 1540, so already in the Ottoman period, the French traveller Pierre Gilles noted that Aspar Cistern was empty. However, it may be suspected that it was not used much earlier because it was known as Xerokepion, or Dry Garden, during the late Eastern Roman Empire.

During the reign of Sultan Suleyman the Magnificent, a small mosque was built within the reservoir, among vegetable gardens. Over time, a small village developed there, surrounded by orchards and gardens. Currently, Aspar Cistern is a recreational area with playing fields and picnic tables.

The final identification of the reservoir, known for many years as Sultan Selim Çukurbostanı due to the proximity of the mosque that bears his name, as Aspar Cistern was only made in the middle of the 20th century, based on an analysis of the Chronicon Paschale record. The work mentions that Aspar Cistern was large and was located near the ancient city walls, i.e., the Walls of Constantine. The only reservoir that meets these conditions is the cistern described above.

This text is a fragment of a guidebook to Istanbul: "Byzantine Secrets of Istanbul".