A castle clock is a clock

Clock

A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

 whose face is mounted outside a castle

Castle

A castle is a type of fortified structure built in Europe and the Middle East during the Middle Ages by European nobility. Scholars debate the scope of the word castle, but usually consider it to be the private fortified residence of a lord or noble...

 or perhaps a church tower. They may be elaborate or simple.

Al-Jazari

Al-Jazari

Abū al-'Iz Ibn Ismā'īl ibn al-Razāz al-Jazarī was a Muslim polymath: a scholar, inventor, mechanical engineer, craftsman, artist, mathematician and astronomer from Al-Jazira, Mesopotamia, who lived during the Islamic Golden Age...

 constructed an elaborate clock and described it in his Book of Knowledge of Ingenious Mechanical Devices in 1206. It was about 3,3 metres high (11 feet), and had multiple functions alongside timekeeping. It included a display of the zodiac

Zodiac

In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...

 and the solar and lunar paths, and a pointer in the shape of the crescent moon

Lunar phase

A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...

 which travelled across the top of a gate

Gate

A gate is a point of entry to a space enclosed by walls, or a moderately sized opening in a fence. Gates may prevent or control entry or exit, or they may be merely decorative. Other terms for gate include yett and port...

way, moved by a hidden cart

Cart

A cart is a vehicle designed for transport, using two wheels and normally pulled by one or a pair of draught animals. A handcart is pulled or pushed by one or more people...

 and causing automatic doors

Gate operator

A gate operator is a mechanical device used to open and close a gate, such as one at the end of a driveway. There are two main types of electric gate openers hydraulic or electromechanical; these can be further slit into the following categories, worm driven, arm openers and underground openers...

 to open, each revealing a mannequin

Mannequin

A mannequin is an often articulated doll used by artists, tailors, dressmakers, and others especially to display or fit clothing...

, every hour

Hour

The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...

. It was possible to re-program the length of day

Daytime (astronomy)

On Earth, daytime is roughly the period on any given point of the planet's surface during which it experiences natural illumination from indirect or direct sunlight....

 and night

Night

Night or nighttime is the period of time when the sun is below the horizon. This occurs after dusk. The opposite of night is day...

 everyday in order to account for the changing lengths of day and night throughout the year, and it also featured five robot

Robot

A robot is a mechanical or virtual intelligent agent that can perform tasks automatically or with guidance, typically by remote control. In practice a robot is usually an electro-mechanical machine that is guided by computer and electronic programming. Robots can be autonomous, semi-autonomous or...

ic musicians who automatically play music when moved by lever

Lever

In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

s operated by a hidden camshaft

Camshaft

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

 attached to a water wheel

Water wheel

A water wheel is a machine for converting the energy of free-flowing or falling water into useful forms of power. A water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface...

. Other components of the castle clock included a main reservoir

Reservoir

A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...

 with a float, a float chamber

Float chamber

A float chamber is a device for automatically regulating the supply of a liquid to a system. It is most typically found in the carburettor of a normally aspirated internal combustion engine, where it automatically meters the fuel supply to the engine...

 and flow regulator

Regulator (automatic control)

In automatic control, a regulator is a device which has the function of maintaining a designated characteristic. It performs the activity of managing or maintaining a range of values in a machine. The measurable property of a device is managed closely by specified conditions or an advance set...

, plate and valve

Valve

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

 trough, two pulley

Pulley

A pulley, also called a sheave or a drum, is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference. A rope, cable, belt, or chain usually runs over the wheel and inside the groove, if present...

s, crescent disc displaying the zodiac, and two falcon automata

Automaton

An automaton is a self-operating machine. The word is sometimes used to describe a robot, more specifically an autonomous robot. An alternative spelling, now obsolete, is automation.-Etymology:...

 dropping balls into vase

Vase

The vase is an open container, often used to hold cut flowers. It can be made from a number of materials including ceramics and glass. The vase is often decorated and thus used to extend the beauty of its contents....

s.