An extremely rare object, almost unique in the world, of particular scientific as well as historical and archaeological interest, is the inscribed marble sphere used as a solar clock.

Found in completely fortuitous circumstances in 1985 during the renovation of some rooms on the ground floor of the Government Palace, it is kept inside the Museo Archeologico delle Marche (‘Archaeological Museum of the Marche’) in Ancona. A reproduction of the globe is also preserved inside the “G. Piermarini” Theatre.

The sphere, with a diameter corresponding almost to a Roman foot (cm 29.3), has engraved signs and letters on its surface:

• in the upper hemisphere, the equator line and a perpendicular meridian are outlined;
• from the pole of the sphere to the equator line runs a row of thirteen holes marked with letters of the Greek alphabet (α, β, γ, etc.) corresponding to the numerals (1, 2, 3, etc.).
• there is also a diagram consisting of three concentric circles with abbreviated and non-abbreviated Greek names indicating the winter solstice, the constellations of the Zodiac and the summer solstice.
• at the bottom there are two recesses, the larger and deeper one was to be used for fixing to a support.

The globe worked by orienting the inscribed face of the sphere to the North and using as an indicator the boundary between the illuminated zone and the shadowed area, which moved to the surface of the sphere. It could thus be used as a calendar, based on the position of the shadow on the concentric circle diagram in the strokes indicated by the zodiac signs, and as a clock following the passage of the shadow over the numbered holes corresponding to daylight hours; the function of showing the temporal relationship between day and night for each time of the year manifested itself through the concentric circles and the arc that intersects them.

It is a sophisticated scientific instrument, which requires mathematical, geometric and astronomical knowledge both during its construction and its use. Although it can function as a common solar clock, the technique used for its realization and the complexity of the information arising from its consultation make it a suitable object for scientific demonstrations.

The basic conception that produced it, the type of marble and the writing make it a Greek product that finds comparisons only in another specimen found in Greece, in the sanctuary of Hera in Prosymna, near Argo.

The interest in this type of instruments and in the scientific principles on which they are based were spread in Rome in the first century B.C., under the impetus of the reform of the calendar introduced by Augustus and the grandiose realization of the clock-calendar of Campo Marzio. The reproduction of spheres very similar to that of Matelica in pictorial and sculptural depictions of the early imperial age have made it possible to identify elements of comparison and to refer Matelica’s spherical solar clock to the 1st-2nd centuries AD: such dating would agree with that of the Roman-era building within which it was found.

If you want to know more, watch the video about the Globe and its 3D reconstruction