Tamaris - The Town on the River Tamar
There are two clues in Ptolemy's Geography (bk.II, ch.ii); near the the beginning of part 2, which reads:
Description of the south side below which is the Oceanus Britannicus [English Channel]. After the Ocrium Promontorium [Lizard Point, Cornwall] is the mouth of the Cenio¹ river 14*003 51? (then) the mouth of the Tamarus² river 15*40 52? (then) the mouth of the Iscas³ river 17*40 52? …
- This river remains unidentified.
- River Tamar, Devon/Cornwall.
- River Exe, Devon.
and also the very last sentence of part 2:
Next to these [the Durotriges], but more to the west, are the Dumnoni, whose towns are: Voliba 14*45 52? Uxella¹ 15*00 52? Tamara² 15*00 52? (and) Isca, where is located Legio II Augusta³ 17*30 52?.
- Vxelis (Launceston, Cornwall); the previous entry Voliba remains unidentified.
- At the mouth of the Tamar near Plymouth.
- Isca Dvmnoniorvm (Exeter, Devon).
The name Tamaris is mentioned in the Ravenna Cosmology (R&C#5) of the seventh century, where it is listed between the entries for Nemetostatio (Nanstallon, Cornwall) and Dvrnovaria (Dorchester, Dorset).
The river-name Tamar is possibly derived from Welsh?Gaelic, possibly meaning 'the dark one' or simply 'the river'. There are several other British rivers whose names have the same root-meaning; the Thames (Latin Tamesis) in London, the Team in County Durham, the Thame in Buckingham/Oxfordshire, and finally the Tame, of which there are three, in Warwickshire/Staffordshire, Yorkshire/Cheshire and North Yorkshire.
References for Tamaris – The Town on the River Tamar
Historical Map and Guide – Roman Britain by the Ordnance Survey (3rd, 4th & 5th eds., 1956, 1994 & 2001); Oxford Dictionary of English Place-Names by A.D. Mills (Oxford 1998).