The Roman Map of Britain Tarvedunum or Orcas promontorium perhaps two separate places Holborn Head and Dunnet Head, Caithness

Tarouedoum h kai OrkaV akra Tarvedum sive Orcas promontorium vars. Tarouhdoumh Tarvedume, Tarouidoum Tarvidum, Taroueda Tarveda (Ptolemy II 3 1)
Meta to Tarouedoum akron h thn Orkada post Tarvedum promontorium sive Orcadem (Ptolemy II 3 4)
Taroaidounou akron thV kai OrkadoV kaloumenhV akraV Taroaedunum promontorium sive Orcas promontorium (Marcianus Heracleensis Periplus Maris Exteri II 45)
Orkan (akrwthrion) Orcadem (Diodorus Siculus History V 21)

commonly considered Dunnet Head, Caithness

    Watson CPNS p36 noted that Macbain thought Tarvedunum prom. either Holborn Head or Dunnet Head. He pointed out that Holborn Head was closer to the river Thurso 'Bull's Water.' Dunnet Head being closer to the Orkneys might be Orcas promontorium; while Holborn Head might be Tarvedunum promontorium - two distinct places, confounded.