The Roman Map of Britain Olenaco Blennerhasset, Allerdale, Cumbria

Olerica (R&C 121) next
Olikana Olicana, var. Olokana Olocana (Ptolemy II 3 10) a polis of the Brigantes
Praefectus alae primae Herculeae, Olenaco var. Elenaco (ND xl₅₅)

   Olerica (R&C 121) is listed between Maio (Maglone) and Derventione (Old Carlisle and Papcastle), and thus can be none else but Blennerhasset (NY1941). Understandably, the three names have been considered by most to be the same; though assigning the name to Ilkley, then Elslack (see PNRB pp 430-1).
    Resolving the three forms to Olenac-o/a is fairly straight-forward. Blennerhasset complies with Ptolemy's assignment to Brigantian territory. The only known conflict is that pottery evidence at the site seems to limit the occupation to the late Neronian and early Flavian period, with no indication of activity during the 4th century as demanded by the current interpretation of the Notitia Dignitatum. This is more of a problem for the interpretation of the Notitia Dignitatum, than for an assignment to Blennerhasset - unless there are two sites named Olenaco. Even if its name was later transferred to the nearby Caermote (NY2036), that site has no record of a late occupation either.
    If it turns out that there are two sites involved, both Olerica and Olenaco (Holder and Whatmough offered oler(i)ca 'swan') still have the potential to be based on Pokorny el-1, ol-, _el- (el- in tree names for `alder', `elm' and `juniper':), specifically alder. The river rises in Uldale Fells Ulvedale 1230, and flows through the valley of Allerdale Alnerdall c1060 (13th c copy), Alredala 1191, Alredale 1221. Also on the Ellen is Aldersceugh NY195415, just east of the fort; and Allerby NY086398 Aylewardby c1275. The frequency of the OE element alre 'alder' (and those compatible with rationalization) suggests that either the alder was common along the banks of the Ellen, or the river-name was taken to mean alder. The palynological record indicates that Alder pollen represented about 40% of all area tree pollen, second only to the Hazel at 50%*. And, there is sufficient similarity between Olenaco and Alauna (the name of the fort at Marysport and its eponymous river - the Ellen) to have been cause for speculation. Does Olerica/Olenaco mean 'alder-place'? Is Alauna the same?
    Blennerhasset NY1941

Blennerhasset Roman fort, 300m south west of Harbybrow
NATIONAL MONUMENT NO: 32849

*The History of the British Flora,  A Factual Basis for Phytogeography, H. Godwin (1956) Cambridge