Thread by @OptimoPrincipi

1) The fascinating Roman grave memorial of Sextus Vettius Geminus, veteran of the Third Augustan Legion based at Lambaesis, Algeria. The stele with its striking portrait is compelling in its own right – but is made even more so by an intriguing added function that it served...

2) Sextus Vettius Geminus lived sixty years and was a veteran of Legio III Augusta, in which he served a crucial role as signifer or standard-bearer. The old, bearded veteran is shown wearing his toga in a powerful frontal portrait that extends beyond the limits of its frame..

3) The memorial to Vettius Geminus was probably set up by his wife Licinia Muciana and a son also called Vettius, whose names are both damaged in the inscription. It is when we look at the top of the gravestone that we see something very surprising...

4) Carved into the top of the gravestone is an intricate sundial, turning the memorial of the Roman veteran into a working clock! Notably, the sundial is engraved at an oblique angle to function precisely in the orientation at which the memorial of Geminus was to be displayed...

5) A number of elements initially suggest that the sundial is an ancient work: the precise engraving of the twelve hour lines, matching Roman numerals, and crucially, the adjustment of the dial plane to fit the stone's exact angle of display, rather than simply moving the stone..

6) It is also hard to resist the poetic use of the memorial to the signifer Geminus – whose raised standard once served as a guide and rallying point for his fellow legionaries – guiding those around him even in death with the raised gnomon of his useful sundial...

7) However, on closer inspection we see that the hours run from VI to VI with XII (noon) in the middle, whereas Romans counted their twelve daylight hours from I to XII. The dial also measures half and quarter hours which is not typical in ancient timekeeping devices...

8) Part or all of the sundial seems, therefore, to be post-Roman in date. Perhaps modernised AM / PM numerals were added to an existing ancient dial at an unknown later date? If someone did repurpose the stone as a sundial, say in the medieval or French colonial periods, then..

9) ..they went to considerable efforts to align the dial to the stone's new display orientation. The wonderful 2nd-century memorial to Sextus Vettius Geminus, topped with its curious sundial, now sits in the epigraphic garden of Lambaesis Archaeological Museum, Algeria.