When did Sarum first get put on the map?
The answer, arguably, is the 3rd C AD but it wasn’t Sarum, it was Sorbiodunum and it wasn’t a map but a list of stopping places with distances between them.
The Antonine Itinerary (Antonini Itinerarium) was an Empire Atlas, named after its supposed patron Antoninus Pius who was the Emperor (138 to 161 AD) and followed Hadrian (each with his eponymous wall). However it was probably compiled after Antoninus’ reign (if only because Britanniarum is plural and Britain wasn’t divided into two provinces till 197 AD). The last itinerary of the British part, the XVth Iter Britanniarum was the route from Silchester (Calleva) to Exeter (Isca Dumnoniorum) via Winchester (Venta Velgarum or Belgarum, Sarum and Winchester were in the Belgae territory), Sarum (Sorbiodunum), Badbury (Vindocladia) and Dorchester (Durnovaria).
The road from Winchester to Sorbiodunum (Sorviodunum) passed through a place called Brige. This site is debated. The route must cross the Test somewhere making Stockbridge a candidate or a little to its south, Horsebridge, another Test crossing and this time on a known Roman road, or Broughton, which has a b, r and g in its name or nearby Buckholt, these all make more geographical sense than an alternative suggestion, Ashley on the New Forest coastline, which would require a loop to the south. The Ordnance Survey map of Roman Britain has it running from Horsebridge across Broughton Hill to Winterslow. Winterslow has also been suggested as a site for Brige. The iter says the distance from Brige to Sorbiodunum 8 miles (a Roman mile is about 0.92 of a modern mile). It is nearer 18 from Stockbridge or Horsebridge though an accidentally omitted x (=10) might explain this. This road remains as the way through Ford to Old Sarum.
The road from Sorbiodunum towards Venta Belgarum (Winchester) in the XVth Antonine Iter Britanniarum
This line continues west to the lead mines of the Mendips. The Antonine XVth journey however then turns south to continue to Badbury (Vindocladia) which it says is about 12 (Roman) miles, it is closer to 23. This line continues a more direct Silchester to Sarum route, from London, missing Winchester out, and approaching Sarum as the Portway. The beginning of this route from Sarum has been lost, it ran across our modern football field, then Castle Keep and across the river, possibly making it the Strœt Ford of our village. A settlement developed along it. Across the river Folly Lane and then Roman Road pick up the line. Sorbiodunum may refer to that settlement rather than the hill fort. There may have been a mansio in that settlement or even up on the hill fort. Mansios were the Roman Premier Inns, stopping places every 25-30 Km. Mansion and remain come from the same Latin stem.
Other Roman or Romanised roads meet at Old Sarum but are not detailed on the Antonine XVth Iter Britanniarum.
The road from Sorbiodunum towards Vindocladia (Badbury) in the XVth Antonine Iter Britanniarum