Elevation of the bronze door to the vestibule of Santi Cosma e Damiano, Rome, after Sangallo's drawing in the Barberini Codex (Rome, Vatican, Biblioteca Apostolica Vaticana, Barb. lat. 4424, fol. 17; for further on copies from the Barberini Codex in the Paper Museum see dal Pozzo A.IX, pp. 479-482). The extant Paper Museum contains a total of 54 copies of architectural drawings from the Barberini Codex. The copies were produced by two draughtsmen, identified in dal Pozzo A.IX as the Codex Ursinianus Copyist and the Sangallo Copyist 2. Virtually all the copies are mechanical 1:1 replicas, probably traced. Annotations and measurements are usually omitted. For further, see A.IX, pp. 479-482. 

The drawing differs considerably from the Sangallo original, which shows only the right-hand leaf set within the architrave doorway. By contrast, the copy shows both leaves and omits the architrave. It also omits the bead-and-disc moulding, which Sangallo correctly shows round the edges of the panels. Both drawings omit the bosses hiding the rivets, which do appear in a drawing Giovanni Battista Montano (also in the Paper Museum; London, Sir John Soane's Museum, vol. 125, fol. 126).

The doors are 4.92m high and 3.16m wide, and guard the entrance to a small domed circular hall, which was originally flanked by two long apsidal halls, one surviving, which projected forward on to the Sacra Via, just east of the Roman Forum. The building dates to the early fourth century, and used spolia for most of its architectural ornaments. The bronze doors appear to be Severan in date (c. 200). The doorway was dismantled in 1632 and reset at a higher level until 1879 when, following excavation, it could be restored to its original level, but the bronze doors themselves are relatively unscathed.

The purpose of the building is not known for certain, but it was probably erected by the Emperor Maxentius (reg. 306–12), perhaps in honour of his deified son Romulus and/or the Penates, and subsequently rededicated under Constantine. The doorway between the circular hall and the contiguous rectangular hall behind, which was part of the Temple of Peace (possibly a library), appears to be original, suggesting that the structure was a monumental entrance/vestibule to the latter, which Pope Felix IV (reg. 526–30) later converted into the basilica of Santi Cosma e Damiano. In the seventeenth century the vestibule was thought to have been a temple of Romulus and Remus, as on the 1550 Lafrery Speculum print which was probably in the Paper Museum, or the Templum Urbis Romae (I. Campbell, ‘Reconstructions of Roman temples made in Italy between 1450 and 1600’, unpublished D.Phil. thesis, University of Oxford, 1984, vol. I, p. 252f.).

Annotations: top, scribal hand] Porta di S. Cosmo e Damiano (‘Door of SS. Cosmas and Damian’)

Text adapted from Ian Campbell, The Paper Museum of Cassiano dal Pozzo: A Catalogue Raisonné. A.IX: Ancient Roman Topography, London, 2004, cat. 182.