| Unit Name: | Cohors I Aelia Dacorum |
| Dates: | AD 117–25 to 400 |
| Country: | Roman Empire |
| Type: | Roman auxiliary cohort |
| Role: | infantry |
| Size: | 800 (until AD 284) |
| Garrison: | Britannia AD 125 – c. 400 |
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. It was first raised by the Roman emperor Hadrian (r. AD 117–38) in the Roman province of Dacia not later than AD 125 and its last surviving record dates 400. It was deployed, for virtually its entire history, in forts on Hadrian's Wall on the northern frontier of Britannia province.
The regiment carries the epithet Aelia, implying that it was either founded, or honoured for valour, by the emperor Hadrian (Publius Ælius Hadrianus).[1] It was probably founded between AD 117 (the date of Hadrian's accession) and c. 125, the date of the unit's first datable attestation.[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). As no record of the unit has been found in Dacia, Holder argues that the regiment was transferred to Britain immediately after it was established. (This was in accordance with a general imperial policy of deploying auxiliary units far from recently conquered (or pacified) regions in order to assure their loyalty: thus, seven British regiments, raised during the Flavian period (71–96), are attested as deployed in Dacia in the reign of Hadrian).[3]
The regiment was probably of milliaria strength (i.e., 800-strong), divided into ten centuriae of 80 men each. Although only one of its records mentions its milliaria status, the latter is supported by the fact that all but the first of its attested commanders carried the title of tribunus, normally an indication of milliaria status.
The fact that the unit's first surviving record (c. 125) attests a Cohors I Dacorum (without the Ælia title), and that its commander at the time, Marcus Cludius Severus, held the rank of praefectus, has led to the suggestion that it was originally a quingenaria regiment (480-strong, divided into six centuriae) and that it acquired its Ælia title when it was upgraded to milliaria status in 127.[4]
There is no evidence that the unit ever acquired a cavalry contingent: in no inscription is the regiment ascribed the epithet "EQ" (for equitata = "equipped with cavalry"), and no cavalry officer (decurion) or trooper (eques) is attested.[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). It was permanently stationed at Fort Banna (Birdoswald, Cumbria), on Hadrian's Wall, from 126 to at least 276/82, where it is attested in numerous inscriptions.[2]
The inscription of 276/82 is one of the latest datable record found which mentions I Aelia Dacorum. However, a later inscription found at Fort Banna, datable to the latter period of the emperor Diocletian's rule (293–305), records that the fort's headquarters buildings, which had fallen into ruins, were rebuilt under the direction of the centurion Flavius Martinus, who is described as praepositus cohortis ("cohort acting-commander"). The fact that the fort was in ruins and then repaired suggests that it may have been abandoned for a period, and then re-occupied. The text is incomplete, therefore it is uncertain whether Martinus commanded I Aelia Dacorum, or some other regiment.
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.[5] This record shows that the regiment was probably present in Britain until the definitive withdrawal of Roman troops from the island in c. 410. By this time, the unit probably contained only c. 300 effectives, around a third of its size in the 2nd century. This reduction was in line with the army in Britain as a whole, which had shrunk from a peak of c. 55,000 in 200 to c. 17,500 effectives in 400.[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. These are headed with the initials "IOM", for Iovi Optimo Maximo ("to Jupiter the Best and Greatest"). One of these was jointly dedicated to Jupiter and to the numen ("Divine Spirit") of the first emperor Augustus, who was officially deified after his death. One altar is dedicated to the Roman god of war Mars and one to the god of the sea, Neptune.
Only one altar was dedicated to a native British deity, the Celtic god Cocidius (after whom the fort occupied by the cohort before Banna was named: Fanum Cocidi, meaning "Shrine of Cocidius", at Bewcastle, Cumbria).[13]
However, these dedications are in no way representative of the religious affiliation of the regiment's members, as they were all erected by the cohort's tribunes (commanding officers). They thus represent the army's official cults. The cohort's soldiers doubtless revered a great variety of British and other native deities.
| c 125 | Marcus Clu(dius?) Severus | Praefectus | Roman knight | Italian | Cesena | Severus, in a funerary stone from Cesena, is described as praefectus of the cohort. Cludius name fits gap in inscription and is attested in votive inscription from Dacia | |
| c. 150 | Ti. Claudius Proculus Cornelianus | Tribunus | Roman knight | prob. Numidian | Previously commanded Cohors II Bracarum (in Moesia Inferior?); subsequently (153-6) commanded Ala Sulpicia in Germania Inferior | ||
| c. 160 | Domitius Honoratus | Tribunus | Roman knight | prob. Bithynian | Prusias ad Hypium? | ||
| 205-7 | Aurelius Iulianus | Tribunus | Roman knight | British? | |||
| 219 | Marcus Claudius Menander | Tribunus | Roman knight | prob. Greek (from Asia Minor) | Ephesus? | A Sextus Claudius Menander attested in Ephesus | |
| 235-8 | Flavius Maximianus | Tribunus | Roman knight | Italian? | Praeneste (Latium)? | evocatus (veteran) of Cohors I Praetoria (cohort of Praetorian Guard) | |
| 237 | Aurelius Faustus | Tribunus | Roman knight | Dacian? | A veteran with same name attested in Dacia | ||
| 258-69 | Marcius Gallicus | Tribunus | Roman knight | ||||
| 258-69 | Probius Augendus | Tribunus | Roman knight | ||||
| 270-4 | Pomponius Desideratus | Tribunus | Roman knight | Gaul? | name attested 6 X in late Gaul | ||
| 276-82 | Aurelius Vinus | Tribunus | Roman knight | ||||
| XXXX | |||||||
| c. 125 | Aelius Dida | Centurion | Roman citizen | ||||
| c. 126 | Decius Saxa | Centurion | Roman citizen? | ||||
| 293-305 | Flavius Martinus | Centurion (of I Aelia Dac.?) | Roman citizen |
| Octavius Honoratus | Tribunus | Roman knight | Numidian? | |||
| Reginius Iustinus | Tribunus | Roman knight | Gaul or Briton? | Acc. to E. Birley, "fabricated" name suggests Celtic origin | ||
| Statius Longinus | Tribunus | Roman knight | Italian? | Canusium? | ||
| Iulius Saturninus | Tribunus | Roman knight | ||||
| Terentius Valerianus | Tribunus | Roman knight | Italian? | Novara? | ?Same as Caius Terentius Valerianus who erected tombstone to son at Novara? | |
| Funisulanus Vettonianus | Tribunus | Roman knight | Italian? | |||
| Ammonius Victorinus | Tribunus | Roman knight | ||||
| Congaonius Candidus | Centurion | prob. Gaul or Briton |
| 205-7 | Aurelius Concordus | child (of tribune Aurelius Iulianus), died at 1 year | Birdoswald | Tombstone, erected by father | |||
| uncertain | Decibalus Blaesus | child, died days after birth child (brother of Decibalus), died at 10 years | uncertain (Dacian name) uncertain (Roman name) | Birdoswald | Tombstone, erected by elder brother |