Astrarium of Giovanni Dondi dell'Orologio

The Astrarium of Giovanni Dondi dell'Orologio was a complex astronomical clock built between 1348 and 1364 in Padova, Italy, by the doctor and clock-maker Giovanni Dondi dell'Orologio. The Astrarium had seven faces and 107 moving parts; it showed the positions of the sun, the moon and the five planets then known, as well as religious feast days. It was one of the first mechanical clocks to be built in Europe.

Dondi documented the Astrarium in detail in the Tractatus astrarii, which is the earliest complete surviving description of its kind; the Albion of Richard of Wallingford predates it, but survives only as fragments. In the introduction, Dondi writes that his machine was built in accordance with the 13th-century Theorica planetarum of Campano di Novara, and to demonstrate the validity of the descriptions of the motion of heavenly bodies of Aristotle and Avicenna. The Tractatus survives in twelve manuscript sources. The autograph in the Biblioteca Capitolare of Padova (MS. D39) and a copy of it, also in Padova, are certainly the work of Dondi. The other sources are rewritten versions of the autograph, to which Dondi's contribution is as yet unclear. The autograph manuscript was published in 1987 in a critical edition with colour facsimile and French translation by Poulle as the first volume of the Opera omnia of Jacopo and Giovanni Dondi.

The astrarium was considered to be a marvel of its day. Giovanni Manzini of Pavia writes (in 1388) that it is a work "full of artifice, worked on and perfected by your hands and carved with a skill never attained by the expert hand of any craftsman. I conclude that there was never invented an artifice so excellent and marvelous and of such genius".

Dondi writes that he obtained the idea of an astrarium from the Theorica Planetarum of Giovanni Campano da Novara, who describes the construction of the equatorium.

The astrarium was primarily a clockwork equatorium with astrolabe and calendar dials, and indicators for the sun, moon, and planets. It provided a continuous display of the major elements of the solar system and of the legal, religious, and civil calendars of the day. Dondi's intention was that it would help people's understanding of astronomical and astrological concepts. (Astrology was then considered a subject worthy of study by the intellectual elite and was taken reasonably seriously.)

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