DÉISI
As a proper noun, the word Déisi (sg. Déis) means
“subject peoples” and was the name borne in the his-
torical period by two important Érainn populations, the
one in Brega, the other in Munster. The former were
known as both the Déisi Breg and the Déisi Temro (the
subject peoples of Tara) because they occupied lands
just south of the ancient site. In the eighth century, their
kingdom was eclipsed by the expanding Southern
Uí Néill dynasty of Síl nÁedo Sláine, though with the
decline of their overlords, they were able to regain their
independence in the eleventh. Their revival, however,
did not outlast the subsequent Anglo-Norman Invasion.
Larger were the Déisi populations in Munster, which
originally formed a single, if discontinuous, conglom-
erate stretching from the extreme southeast to the north
of the province. In the fourth or fifth century, a branch
of the Déisi from the Waterford area established a
colony in Dyfed (southwest Wales), where they
retained power until the tenth century. Later, their Irish
counterparts split into two main divisions about the
beginning of the eighth century: The Déisi Muman
lived in County Waterford and southern Tipperary and
the western Déisi in eastern Limerick. In the latter ter-
ritory, the most important people were the Déis Tuais-
cirt, who conquered east County Clare. By the early
tenth century, they adopted the name Dál Cais and
subsequently became the most powerful kingdom in
Ireland, under their ruler Brian Boru (d. 1014).
D
AN
M. W
ILEY
References and Further Reading
Byrne, Francis John.
Irish Kings and High-Kings
, 2nd ed. Dub-
lin: Four Courts Press, 2001.
Jackson, Kenneth.
Language and History in Early Britain
. Edin-
burgh: Edinburgh University Press, 1953.
Ó Corráin, Donncha.
Ireland before the Normans
. Dublin: Gill
and Macmillan Ltd, 1972.
See also
Dál Cais; Érainn; Munster;
Southern Uí Néill
DERBFORGAILL
Derbforgaill (1108–1193), daughter of Murchad Ua
Máelsechlainn, king of Mide, and wife of Tigernán Ua
Ruairc, king of Bréifne, owes her place in history
mainly to her abduction at the hands of Diarmait Mac
Murchada, king of Leinster. Following an internal
Leinster rebellion against Mac Murchada more than a
decade after the abduction, Ua Ruairc seized the chance
to avenge his insulted honor and marched on Mac
Murchada, expelling the Leinster king across the Irish
Sea. Mac Murchada’s subsequent recourse to foreign
military aid in regaining his kingdom brought about the
Anglo-Norman invasion. Surveying this chain of events,
contemporary and later observers laid the blame for the
invasion at Derbforgaill’s feet, dubbing her the Irish
Helen of Troy. Different sources have attributed varying
motivations for the abduction, including revenge and
overweening lust. Given the circumstances surrounding
the kidnapping, however, which occurred in Mide in
1152 following Tigernán’s temporary deposition as king
of Bréifne by Diarmait and Tairrdelbach Ua Conchobair,
it is likely that political motivations were at least partly
at play. Mac Murchada and Ua Ruairc were competitors
in the territorial dismemberment that took place in
Derbforgaill’s homeland of Mide following that king-
dom’s twelfth-century collapse as a major power. In
addition to representing a dramatic undermining of Ua
Ruairc’s authority, it has accordingly been suggested
that Derbforgaill’s seizure may have symbolized Mac
Murchada’s pretensions toward Mide. Some sources
report that Derbforgaill’s brother Máel-Sechnaill col-
luded with Mac Murchada in arranging the abduction;
possibly Máel-Sechnaill, who had newly come into
power in the eastern portion of Mide, felt his best chances
for survival lay in an alliance with Mac Murchada.
Derbforgaill’s own role in the kidnapping has been a
further matter of dispute, with some sources portraying
her as an innocent victim led to the kidnapping site by
her brother. Others, no doubt influenced by the report
that Derbforgaill was accompanied into captivity by all
her cattle and her wealth, accuse her of having been
complicit in the affair. Complict or not, however,
through the intervention of Tairrdelbach Ua Conchobair,
Derbforgaill, her cattle, and her wealth returned to Ua
Ruairc within the year.
That wealth must have been fairly considerable, for
in 1157 Derbforgaill is recorded as donating a large sum
of gold to the newly consecrated monastery of Mellifont
in Drogheda. While Mellifont had links to Ua Ruairc,
Derbforgaill was also a generous patron of churches
associated with her own family. In 1167, she finished
the Nuns Church at Clonmacnoise, a foundation linked
to the Arroasian convent at Clonard where her cousin
Agnes was abbess. Derbforgaill retired into religious
life in Mellifont in 1186, dying there seven years later
at the age of eighty-five. Although she is the single most
historically documented woman in pre-Norman Ireland,
there is no record of Derbforgaill’s having had any
children. The fact that Tigernán had a son called Máel-
Sechnaill, a name with strong family links to Derbfor-
gaill not hitherto seen in the Ua Ruairc genealogies,
may, however, indicate she had at least one child.
A
NNE
C
ONNONReferences and Further Reading
Byrne, Francis John.
Irish Kings and High-Kings. London:
Batsford, 1973.
DÉISI