The Milion was the mile marker in Constantinople, located near the Augustaion and Hagia Sophia. It marked the beginning of the Mese, the central avenue of Constantinople. Probably dating to the reign of Constantine (d. 337), it played a role in reinforcing the romanitas of the new capital, as it was modeled on the Miliarium Aureum. Just as the Miliarium Aureum in old Rome, the Milion originally marked the start of all roads throughout the empire, symbolically evoked the entire Roman world and Constantinople’s place in it.

The Milion was a tetrapylon adorned with statues, including a Tyche, Constantine I and St. Helena. Two equestrian statues of Trajan and Hadrian (or possibly Theodosius II) were also erected nearby. Later a horologion was constructed nearby by Justinian (527-565), while Justin II (565-578) erected statues of his wife Sophia, his daughter Arabia and his nephew Helen there.

As one of the major centers of the city, it often played an important role in the city. Emperors were hailed by the Blues at the Milion during imperial processions. During the Iconoclastic controversy, Constantine V (741-775) reportedly removed depictions of ecumenical councils and replaced them with scenes from the Hippodrome that included his favorite charioteer. It apparently was the occasional location of executions, while it played an important role in the fighting between Nikephoros III Botaneiates and Alexios Komnenos . After being damaged or even destroyed during the Fourth Crusader, the region then came under the jurisdiction of Hagia Sophia. Any surviving remains seem to have been destroyed during the construction of Ottoman waterworks. Ruins of a structure uncovered in 1967/68 near an Ottoman water siphon (Turkish su terazisi) are generally identified as the remains of the Milion.