This is the precious fragment of a clock in which the slow dripping of water from the basin marked the passage of the hours. On the inside, twelve columns – only seven are left – of circular notches show the hours month by month. On the outside, the figure of a tutelary deity corresponds to each month’s column. The deities face each other two by two, with the image of the pharaoh between them. This water clock, in black granite, was produced by craftsmen in Alexandria during the Ptolemaic period and found in Rome in the part of the Campo Marzio where a temple of Isis once stood.