UA BRIAIN, MUIRCHERTACH (1050–1119)
Osraige, Mide, Connacht, and Dublin to Ardee, County
Louth, to gain submission from the Airgialla and
Ulaid; the former stood their ground at Ard Monann
(unidentified) where they slaughtered the Munstermen
under Muirchertach, described as rígdamna Muman,
“makings of a king of Munster” (AFM). In the same
year, his father appointed him king of Dublin with
which he was sporadically associated for the rest of his
life. He then disappears without a trace until October 29,
1084 when he and the forces of Dublin, Leinster,
Osraige, and Munster defeated Donnchad Ua Ruairc
of Uí Briúin Bréifne at Móin Cruinnióce, near Leixlip,
County Kildare (a Norse settlement which he may
have ruled from Dublin). In this major battle 4,000
were killed, Muirchertach cutting off Ua Ruairc’s
head and bringing it back to his father’s palace at
Limerick.
When Tairrdelbach died in 1086, Munster was
divided between his three sons, Tadc, Diarmait, and
Muirchertach. Tadc died within a month, and
Muirchertach banished Diarmait and seized the whole
province. In 1087, he fought a battle against Diarmait
and the king of Leinster at Ráith Étair (possibly the
promontory fort at the tip of Howth Head), and
Muirchertach’s forces triumphed. In 1088, he sent one
fleet up the Shannon as far as Incherky, south of Clonfert,
where the king of Connacht, Ruaidrí na Saide Buide
Ua Conchobair, father of the great Tairrdelbach,
slaughtered Muirchertach’s men. Another Munster fleet
sent around the west coast was also slaughtered, the
Connacht army then invading Corco Mruad (the Burren,
Co. Clare).
Domnall Mac Lochlainn, king of the Northern
Uí Néill, now emerged as Ua Briain’s rival for
supremacy, allying with the sons of Muirchertach’s
uncle Donnchad mac Briain (d. 1064) by marrying
the daughter of his grandson Cennétig (d. 1084),
who had been king of Telach Óc in Tír nEógain with
Mac Lochlainn’s support. In 1088, the latter
attacked Connacht and forced its king to submit, and
then together they marched on Munster in Ua Briain’s
absence in Leinster; Limerick, Kincora, and Emly
were burned and 160 hostages seized, whom
Muirchertach later bought back with cattle, horses,
gold, silver, and meat, victory being symbolically
sealed when the severed head of Donnchad Ua Ruairc
was brought back to Connacht. A Munster source claims
that Ua Briain avenged himself in 1089 by invading
Mide and Leinster, whose king he killed, making him-
self king of Leinster and Dublin, before proceeding to
Connacht to cut down the sacred inaugural tree of the
Connachtmen. Other annals suggest Muirchertach did
not gain the kingship of Leinster and Dublin and had
no role in killing the Leinster king (apparently assas-
sinated by kinsmen), a version of events borne out by
the fact that his men burned Lusk in Fine Gall, killing
160 church occupants, suggesting that it (and presum-
ably Dublin) was in enemy hands.
Also in 1089, Muirchertach sailed to Lough Ree
and looted its islands, but Ua Conchobair blocked the
Shannon near Clonmacnoise, denying the Munster
ships a route home. Driven back to Athlone, they
were forced to surrender both ships and supplies to
the king of Mide, Domnall Ua Máel Sechnaill, return-
ing home under safe conduct overland while the
Connacht and Mide armies sailed the confiscated ves-
sels southward, purportedly reducing the Plain of
Cashel to a desert. In 1090 Ua Briain, Mac Lochlainn,
Ua Conchobair, and Ua Máel Sechnaill held a con-
ference that resulted in the three other kings giving
hostages (presumably in submission) to Mac
Lochlainn, before departing in peace. But Muirchertach
was on the march again in Mide that same year,
though he was defeated by Ua Máel Sechnaill who
invaded Munster, as did Ua Conchobair at about the
same time. Ua Briain then marched into Connacht,
raided Leinster along with the men of Dublin (which
he had obviously retaken), and marched to Athboy in
Brega, where Mac Lochlainn apparently aided him
against Ua Máel Sechnaill.
Ua Conchobair invaded Munster again in 1091 but
was blinded in the following year, whereupon
Muirchertach led an army into the province, took its
hostages, and, according to the Inisfallen Annals,
assumed the high kingship of Connacht. In 1092, Ua
Briain expelled (temporarily) the ruling dynasty of
Connacht into Tír nEógain, and the king of Mide came
to Limerick to submit to him, while in 1094 he unprec-
edentedly partitioned Mide between two rival mem-
bers of the Uí Máel Sechnaill. His contemporary power
is evident from the request by the nobility of Man and
the Isles to provide a ruler following their king’s death
in 1095, whereupon Muirchertach apparently found an
outlet for the wayward energies of his nephew, Domnall
mac Taidc, by dispatching him to Man. Two ominous
expeditions by the Norse king Magnus III (“Barelegs”)
in 1098 and 1102–1103, were skillfully handled by Ua
Briain, who bought off Norse aggression in 1102 by
marrying his daughter to Magnus’s younger son
(though the threat dissipated following Magnus’s
killing by the Ulaid in 1103). He likewise improved
relations with the Normans of South Wales when, in
1101, another daughter was married off to Arnulf de
Montgomery, then in rebellion against the new English
king, Henry I: when the latter responded with a trade
blockade, Muirchertach apparently relented, but Arnulf
is said to have fled to Ireland hoping to succeed him
as king, and Muirchertach later wrote to Anselm of
Canterbury thanking him for interceding with Henry
on his son-in-law’s behalf.