The Prague Astronomical Clock, or Prague Orloj is a medieval astronomical clock located in Prague, the capital of the Czech Republic.
The clock was first installed in 1410, making it the third-oldest astronomical clock in the world and the oldest clock still operating.
The Orloj is mounted on the southern wall of Old Town Hall in the Old Town Square. The clock mechanism has three main components — the astronomical dial, representing the position of the Sun and Moon in the sky and displaying various astronomical details; statues of various Catholic saints stand on either side of the clock; “The Walk of the Apostles”, a clockwork hourly show of figures of the Apostles and other moving sculptures, notably a figure of a skeleton, representing Death, striking the time; and a calendar dial with medallions representing the months.
The oldest part of the Orloj, the mechanical clock and astronomical dial, dates from 1410 when it was made by clockmaker Mikuláš of Kadaň and Jan Šindel, then later a professor of mathematics and astronomy at Charles University. The first recorded mention of the clock was on 9 October 1410. Later, presumably around 1490, the calendar dial was added and the clock facade was decorated with gothic sculptures.