SWIMMING ON MERCURY UNDER THE MOON. BIRKAT AL-ZI'BAK AT THE HUMARAWAYH PALACE IN AL-QATA'I ' 1 The article analyzes the references found in Arabic medieval sources (al-Makrizy, Ibn Dukmak Ibn Iyas, Ishaqi) about a pool filled with mercury ("Birkat az-Zi'bak"), which was arranged in the palace of the Tulunid ruler Humarawayh (884-896) in al-Kata'i' in order to cure Humarawayh from cancer. insomnia. According to the testimony of al-Makrizi (1364-1442), the reservoir measured 50x50 cubits (approx.25x25 m), but the depth of the pool is not mentioned in the text. The article critically analyzes the extant information about the existence of mercury pools in the palaces of Muslim rulers, and suggests several hypotheses for the design of the pool in the Humarawayha palace. Key words: Egypt, Tulunids, Humarawayh, al-Kata'i, mercury basin. In 868, the Abbasid caliph al-Mu'tazz appointed General Bakbak governor of Egypt. Ahmed Ibn Tulun, the son of a Turkic slave sent as a gift to the Abbasid ruler from Bukhara, a hereditary professional soldier who was brought up at the Caliph's court in Samarra, was assigned to help him [Hassan, 1986, p.278]. According to the caliph's plan, he was supposed to represent the financial interests of the central government in the province [Filshtinsky, 2006, p. 145]. His ambition, natural intelligence, ability to weave and unravel intrigues, and bravery allowed him to become the head of the country in a ten-year period, having dealt with numerous rivals. In 879-880. Ibn Tulun appropriated the right of khutbah and sikkah, which was considered in the Muslim world as external signs of the sovereign's independence [Barthold, 1966, p. 27]. Ibn Tulun managed to create a powerful navy, an army consisting of Turkic, Berber and Sudanese mercenaries, and carry out agrarian and administrative reforms [Hassan, 1986, p. 278]. In fact, Ibn Tulun turned Egypt into an independent emirate of the Tulunids, who ruled the country from 868 to 905. [Filshtinsky, 2006, ... Read more