This column of green marble in the corner of the stone wall of the Şehzade Mosque in Istanbul is mentioned in the text of the famous seventeenth-century Ottoman traveller Evliya Çelebi. Çelebi writes that the architect Sinan set it up before building the

This column of green marble in the corner of the stone wall of the Şehzade Mosque in Istanbul is mentioned in the text of the famous seventeenth-century Ottoman traveller Evliya Çelebi. Çelebi writes that the architect Sinan set it up before building the mosque exactly in the centre of Istanbul. It is believed that on this spot there once stood a special marker, erected in the Byzantine period, at what the scholars of the time calculated to be the very centre of Constantinople. To make this sign more durable, Çelebi says, a marble column was set up here, which, moreover, could be turned by means of two metal levers, one at the bottom and one at the top, until the level of the street rose so far that turning it became impossible