Numbered at lower center, in graphite, "101 (?)".
This is a depiction by a member of Piranesi's workshop of the Roman Altar with Selene (Luna), the Dioscuri, Phosphoros (the Morning Star), and Hesperos (the Evening Star) now in the Louvre, inv. Ma508, but in Piranesi's time at the Villa Borghese. For another study of the same object, see Bernardino Ciferri's drawing at the British Museum, inv. 2103,5015.2.80. The work also appears as plate 21 of Winckelmann's "Monumenti Antichi Inediti" of 1767.