The Forum of the Ox (Latin: Forum Bovis, Greek: ὁ Bοῦς, meaning "the Ox") was a public square (Latin: Forum) in the city of Constantinople (today's Istanbul). Used also as place for public executions and torture, it disappeared completely after the end of the Byzantine Empire.
The Forum lay along the southern branch of the Mese Odós (the main street of the city), in the valley of the Lycus creek, between the seventh and the third hills of Constantinople. Administratively, it was included in the eleventh Regio of the city, and its site is today located in the neighborhood of Aksaray.
This square was possibly part of Constantine the Great's original city plan design; like the other fora of Constantinople, it was certainly built sometime in the 4th century. The name of the square originated from a large, hollow bronze statue representing the head of an ox. The statue, brought to Constantinople from Pergamum in Asia Minor, was used both as a furnace and a device implementing the brazen bull torture: people were closed inside the ox, which then was heated until they suffocated and burned. During the first persecution of Christians in Asia Minor under Emperor Domitian (r. 81–96) the Ox, still in Pergamum, was used to execute Saint Antipas. According to the Patrologia Latina, in the reign of Julian the Apostate (r. 361–363) many Christians were burned inside the Bull, at that time already moved to Constantinople. In 562 the Forum, at that time surrounded by warehouses and workshops, burned down. The body of the usurper Phocas (r. 602–610) was also incinerated in the ox's head following his deposition. According to some sources, Emperor Heraclius (r. 610–641) melted the statue to mint bullion coins needed to pay his army for his war against the Persians. However, this is not certain since executions using the Ox continue to be attested after Heraclius's reign, for example when Justinian II (r.685-695; 705-711) let burn in the Ox the two Patricians Theodoros and Stephanos, both involved in a failed plot against him. The same Emperor enlarged and adorned the square. During the Byzantine Iconoclasm, Saint Theodosia (d. 729) and Saint Andrew of Crete (d. 766), both defenders of icon veneration, were executed in the square. The former was executed by having a ram's horn hammered through her neck.