The Prague Astronomical Clock (Orloj) is a medieval astronomical clock in Prague and is mounted on the southern wall of Old Town City Hall in the Old Town Square. It is composed of three main components: the astronomical details, “The Walk of the Apostles”, and a calendar dial with medallions representing the months. The oldest part of the Orloj dates back to 1410 when it was made by clockmaker Mikulas of Kadan and Jan Sindel.