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Multa variaque genera sunt horologiorum… [1]
The Museum of the Abbazia di S.Nilo in Grottaferrata was closed some time ago to carry out restoration works and scientific studies of the archaeological finds, [2] as well as to improve the display organization.
This museum houses a rare example of Roman-time sundial. (fig. 1) [3].
Fig. 1: Sundial of Grottaferrata, sides West and South. Fig. 2: A pelecinum dial. Fig. 3: Sundial from Aquileia Museum.
It was made out of a single Proconnesian marble block, of microasiatic origin. It is disc-shaped with two flat surfaces, only slightly raised with respect to the outer rim. The corbel at the base gives its vertical position, and there is still a trace of the sockets used to secure it to an underlying support – now lost – to assure elevation and visibility.
The commonest types that spread in the Mediterranean area toward the end of 1st century B.C. [4], and have come to us are examples with vertical or horizontal installations and with a pelecinum dial, [5] (fig. 2),
or made with a concave hemispherical surface and therefore called hemicyclium dial (fig. 3).
However, “our” sundial is a peculiar one; it can be classified as “bilateral” for the fact that time can be read from both sides. [6]
The flat surfaces of this solar instrument have been carved and “rubricated” (i.e., coloured in red) to make their reading easier, since they acted as sequential dials. This means that a dial is designed to be faced to the East, in order to show the morning hours, whereas the other is faced to the West and shows the afternoon hours (fig. 1) [7].
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