 It and is located on an ancient road between the Roman Forum and Forum Boarium, along the north-western foot of the Palatine Hill.It may first have been built as early as the 6th century in the ruins of the granaries of Agrippa.The unusual round shape suggests it may have been built into the ruined shell of a temple similar in construction to the well-preserved "nymphaeum" once identified as the Temple of Minerva Medica.