The Astrarium
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".
de' 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. de' 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.)
Read more about this topic: Giovanni Dondi Dell'Orologio