The oldest depictions of crucifixion or a cross that I know of.
(1) This is a little-known fresco in Rome dating from somewhere around the 2nd-1st century BC showing a bearded, naked man bound onto a horizontal beam - a patibulum - with some kind of fetter. This would make it one of our oldest known artistic depictions of a crucifixion or at least, a crucifixion-related punishment (predating Jesus even).
(2) This is a late 1st century graffiti found in Pompeii. It shows what seems to be a Latin cross, plus a sort of ledge with a stake attached midway through it, with the letters VIV above it. The graffiti as a whole is often interpreted as a sentence: vivat crux. While a few former scholars interpreted this as a Christian acclamation, it’s more likely that this was a crude insult: “May you live on the cross.” (In other words, may you suffer long and hard.)
(3) This meanwhile is another graffiti scratched in a wall in Pozzuoli (ancient Puteoli) in southern Italy. What’s interesting about this drawing is that near it is scratched a name: Alcimilla. Since this is a woman’s name, either (if we suppose this name is a caption to this drawing) this drawing actually depicts a crucified woman or, a man given a woman’s name as a mocking gesture. this sketch shows the victim hanging, with arms widespread, on a T-shaped cross.
The subject’s legs are wide open, with his/her feet seemingly separate and straddling the vertical beam. Notably, the victim is shown to ‘sit’ on a kind of ledge (there’s that ‘seat’ again).
(4) This is the famous Alexamenos graffiti from Rome (2nd-3rd century). The crucified figure is here shown with a donkey’s head, crucified on a T-shaped cross, with feet separate from each other (and seemingly resting on a footrest). To the left of this figure is a young man, raising one hand in a gesture possibly suggesting worship. Beneath the cross there is a caption written in crude Greek: Αλεξαμενος σεβετε Θεον “Alexamenos, worship god.” However, it has been suggested that σεβετε should be understood as a phonetic misspelling of σεβεται, ‘worships’. As a result, the full inscription would then be translated as “Alexamenos worships a god” or “Alexamenos worships [his] god.”
The inscription, believed to be one of, if not the, earliest pictorial representations of the crucified Jesus, is usually thought to be a mocking depiction of a Christian in the act of worship.
(5) And this is a carved gemstone (an amulet of some sort) from the 2nd-3rd century showing the crucified Jesus. Jesus here is depicted as crucified on a T-shaped cross, completely naked, resting/sitting on a short ledge (hey, there it is again!) midway through through the vertical post, with His feet not nailed, but dangling freely. In fact, Jesus’ hands do not seem to be nailed in this depiction either, but simply tied to the patibulum.