Cohors PrimÆ Ælia Dacorvm (Latin name for "1st Aelian Cohort of Dacians") was an infantry regiment of the Auxilia corps of the Imperial Roman army.

[2] The Dacorum name suggests that its initial recruits were mainly ethnic Dacians from Moesia and/or the recently conquered Roman province of Dacia (annexed in 106 by Hadrian's predecessor, Trajan).

[4] The regiment was transferred from Dacia to Britain not later than 125, when it was stationed briefly at Fort Fanum Cocidi (Bewcastle, Cumbria) and appears to have participated in the excavation of the so-called Vallum, a huge ditch running along the near side of Hadrian's Wall (constructed 122–8).

The regiment is recorded in the Notitia Dignitatum, a late 4th-century official document which contains a list of Roman military units in existence around AD 400, as stationed at Camboglanna (Castlesteads, Cumbria), the fort on Hadrian's Wall neighbouring Banna to the west.

[6] In view of its size and long-term stationing on the northern British frontier, facing the unconquered Caledonia (Scotland), the regiment almost certainly participated in all the major campaigns recorded in this turbulent region, including: The epigraphic record shows that, during the 2nd and 3rd centuries, the regiment won five more imperial titles, presumably for valour, or for loyalty to the awarding emperor:[11] The awards show that, in the period 260–74, the regiment gave its allegiance to the "Gallic" emperors Postumus and Tetricus I, who ruled the breakaway western section of the Empire (comprising Gaul, Spain and Britain), known as the "Gallic Empire".

Of the 27 stone altars found at the cohort's long-term fort (at Birdoswald, Cumbria), 24 are dedicated to Jupiter, the highest Roman god, originally the supreme sky-god of the Indo-Europeans.