This unit was a one-thousand strong infantry unit levied from among the various Celtic tribes of the Roman province of Dacia, which lay in the region of modern eastern Romania, including parts of south-eastern Hungary and northern Yugoslavia. The unit is attested in numerous inscriptions from Birdoswald in Cumbria, all dating from the early third century, on an altarstone dedicated to Jupiter from Bewcastle, also from a single undated building inscription from the vallum to the rear of Hadrian's Wall, between Turret-7b and Milecastle-8. They are also possibly mentioned on a tombstone from High Rochester, north of the Wall, but the unit name may equally be Cohors I Dalmatarum.

Evidence for the Cohort in Britain

1. Bewcastle (RIB 991 altar).
2. High Rochester (RIB 1289 tombstone poss. Coh I Dalmatarum).
3. Hadrian's Wall between Benwell and Rudchester (RIB 1365; 1392).

Cohors Primae Aelia Dacorum - The First Aelian Cohort of Dacians

This unit is believed to be synonymous with Coh I Dacorum.

4. L'Année Épigraphique 1997.1779b; diploma dated c.AD126.
5. L'Année Épigraphique 1997.1001; diploma dated 27th February AD158.
6. Birdoswald (RIB 1872, 1874-1894, altars; 1875 AD237; 1883 AD258-268; 1885 AD270-273; 1886 AD258-268; 1893 AD238-244; 1896 altar AD235-238; 1898 altar; 1904 statue base; 1906 base; 1909 AD205-208; 1914 c.AD219; 1918; 1921 tombstone; 1929a altar AD235-238; 1929b altar AD276-282; Notitia Dignitatum).