In late December 999 AD Brian Bóruma, king of Munster, decisively defeated the Vikings of Dublin[i] at the battle of Glen Máma[ii]. This bloody contest was a severe set-back for the Hiberno-Norse inhabitants of the city, and their king, Sitric Silkbeard, was forced to flee. The following day Brian’s troops marched on Dublin, which they entered uncontested, plundering and burning as they went. However, somewhat unusually, Brian diverted a section of his forces to a forest close to the city. Here they proceeded to cut and burn the trees of Caill Tomair, in an act that was deemed worthy of being recorded in the Irish Annals[iii].

The etymology of Caill Tomair may give an insight into why Brian carried out this unusual manoeuvre. It appears to be made up of the Irish word for a forest/wood (coill) and an Irish rendering of the divine name Thor (Þórr), literally Thor’s Wood[iv]. If this interpretation is correct then it suggests that the site was probably a sacred grove where the pagan inhabitants of Dublin worshipped Thor[v] . If this was the case then its destruction was an act imbued with both religious and political symbolism and a very clear assertion of Brian Bóruma’s dominance over the newly captured city.

Sacred groves played an important part in Norse pagan religious practice and were normally referred to as lundr in Old Norse. These sites appear to have been relatively common and were often incorporated in later Scandinavian place-names. For example Þórs lundr (Thor’s Grove) is a common place-name in Denmark.

The most famous surviving description of a sacred grove comes from an 11th century account by Adam of Bremen, which details the temple site at Gamla Uppsala in Sweden. In it he states that ‘near the temple is a sacred grove which each and every tree is sacred and in which the human and animal victims are hanged’[vi]. This appears to describe the Norse pagan practise of blót , which involved sacrificing animals and sometimes humans, to appease the gods. This ritual was often associated with sacred groves and it is possible that it was also carried out at Caill Tomair in Dublin.

The dedication of the Dublin grove to Thor is not surprising as this deity was one of the most popular Nordic gods. Associated primarily with thunder and fertility, his adherents often wore miniature Thor’s hammers in attempt to invoke his favour. A number of these small hammers are known from Viking Age Dublin and it appears that the city’s residents may have had a special affinity with the thunder god. This is suggested by a number of early Irish texts, which refer to Dublin’s inhabitants as ‘Muintir Tomar’[vii], which probably translates as ‘Thor’s people’.

Furthermore, one of the city’s main pieces of regalia during the 10th century was an object known as ‘Fail Tomar’[vi] or ‘Thor’s Ring’. This item, which was captured by Máel Sechnaill mac Domnaill, king of Mide, in 995 AD, may have been a heathen cult object similar to the Thor’s ring described in the Kjalnesinga Saga. This Icelandic text describes a large ring, which was located within a temple dedicated to Thor. ‘On the altar was to lie a great armband, made of silver. The temple priest was to wear it on his arm at all gatherings, and everyone was to swear oaths on it whenever a suit was brought’[ix]. The use of this Thor’s ring in oath-swearing ceremonies mirrors contemporary Irish society where saint’s relics were often used for pledging oaths and making legal treaties.

Thor’s hold on Dublin was soon to wane, however, and in the early 11th century the city officially became a Christian one. In 1028 its king, Sitric Silkbeard, formally established the diocese of Dublin and Dúnán was ordained the city’s first bishop. Construction also commenced on Christchurch Cathedral and this soon became the focal point of religious practice within the city walls. The citizens of Dublin, it seems, were no longer the people of Thor.

Footnotes

[i] The army facing Brian and his ally Máel Sechnaill mac Domnaill, king of Mide, was a combined force of Dublin Vikings and Leinster men under the command of Máel Mórda mac Murchada

[ii] For a detailed description of the battle see MacShamhráin, A. ‘The battle of Glen Máma, Dublin’in Sean Duffy (ed.) Medieval Dublin II, Dublin, pp. 53-64

[iv] See Downham, C. ‘Religious and Cultural boundaries between Vikings and Irish: The Evidence for conversion‘ & Sayers, W. 1991. ‘Clontarf, and the Irish Destinies of Sigurdr Digri, Earl of Orkney, and Porsteinn Sidu-Hallsson’ in Scandinavian Studies (Spring 1991), p. 176, for discussion

[v] It is also possible, though less likely, that Tomair represents a corruption of a Norse personal name

[vii] Annala Rioghachta Eireann: Annals of the Kingdom of Ireland by the Four Masters, ed. and trans. John O’Donovan, second edition, 7 vols (Dublin: Hodges, Smith, 1856), II, 652-53. & Lebor na Cert: The Book of Rights, ed. and trans. M. Dillon (Dublin: Irish Texts Society, 1962), p. 10 (after Downham, C. ‘Religious and Cultural boundaries between Vikings and Irish: The Evidence for conversion’)