was a cross-piece attached either at the top to give the shape of a T (crux commissa) or just below the top, as in the form most familiar in Christian symbolism (crux immissa). The most ancient image of a Roman crucifixion depicts an individual on a T-shaped cross. It is a graffito found in a taberna (hostel for wayfarers) in Puteoli, dating to the time of Trajan or Hadrian (late 1st century to early 2nd century AD). Second-century writers who speak of the execution cross describe the crucified person's arms as outstretched, not attached to a single stake: Lucian speaks of Prometheus as crucified "above the ravine with his hands outstretched". He also says that the shape of the letter T (the Greek letter tau) was that of the wooden instrument used for crucifying. Artemidorus, another writer of the same period, says that a cross is made of posts (plural) and nails and that the arms of the crucified are outstretched. Speaking of the generic execution cross, Irenaeus (c. 130–202), a Christian writer, describes it as composed of an upright and a transverse beam, sometimes with a small projection in the upright. The New Testament writings about the crucifixion of Jesus do not specify the shape of that cross, but the early writings that do speak of its shape liken it to the letter T. William Barclay notes that, because the letter T is shaped exactly like the crux commissa and because the Greek letter T represented the number 300, "wherever the fathers came across the number 300 in the Old Testament they took it to be a mystical prefiguring of the cross of Christ". The earliest example, possibly of the late first century, is the Epistle of Barnabas. Clement of Alexandria (c. 150 – c. 215) is another early writer who gives the same interpretation of the numeral used for 300. Justin Martyr (c. 100–165) sees the cross of Christ represented in the crossed spits used in roasting the Passover Lamb: "That lamb which was commanded to be wholly roasted was a symbol of the suffering of the cross which Christ would undergo. For the lamb, which is roasted, is roasted and dressed up in the form of the cross. For one spit is transfixed right through from the lower parts up to the head, and one across the back, to which are attached the legs of the lamb."