Sechnassach mac Blathmaic (died 671) followed his father Blathmac mac Áedo Sláine

Blathmac mac Áedo Sláine

Blathmac was a son of Áed Sláine. According to the Irish annals he was High King of Ireland.-Sons of Áed Sláine:Blathmac's father Áed Sláine was a son of Diarmait mac Cerbaill, the apical ancestor of the southern branches of the Uí Néill kindred which dominated Ireland from the late 6th century...

 (died 665) and uncle Diarmait mac Áedo Sláine

Diarmait mac Áedo Sláine

Diarmait was a son of Áed Sláine. According to the Irish annals he was High King of Ireland.-Sons of Áed Sláine:Diarmait's father Áed Sláine was a son of Diarmait mac Cerbaill, the apical ancestor of the southern branches of the Uí Néill kindred which dominated Ireland from the late 6th century...

 (died 665) as High King of Ireland

High King of Ireland

The High Kings of Ireland were sometimes historical and sometimes legendary figures who had, or who are claimed to have had, lordship over the whole of Ireland. Medieval and early modern Irish literature portrays an almost unbroken sequence of High Kings, ruling from Tara over a hierarchy of...

 and King of Brega. He belonged to the Síl nÁedo Sláine

Síl nÁedo Sláine

Síl nÁedo Sláine is the name of the descendants of Áed Sláine , son of Diarmait mac Cerbaill. Part of the Southern Uí Néill—they were the kings of Brega—they claimed descent from Niall Noígiallach and his son Conall Cremthainne....

 kindred of the southern Uí Néill

Uí Néill

The Uí Néill are Irish and Scottish dynasties who claim descent from Niall Noigiallach , an historical King of Tara who died about 405....

, named from his grandfather Áed Sláine

Áed Sláine

Áed mac Diarmato , called Áed Sláine , was the son of Diarmait mac Cerbaill. Legendary stories exist of Áed's birth. Saint Columba is said to have prophesied his death...

 (died 604).

Sechnassach's father and uncle are said to have died in a great plague—the buide Chonaill—which struck Ireland

Ireland

Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

 from 664 or 665 onwards.

While the Baile Chuinn Cétchathaigh, compiled in the reign of Fínsnechta Fledach

Fínsnechta Fledach

Fínsnechta Fledach mac Dúnchada was High King of Ireland. Fínsnechta belonged to the southern Síl nÁedo Sláine sept of the Uí Néill and was King of Brega, in modern County Meath, Ireland. He was a grandson of Áed Sláine. His father Dúnchad had died in 659...

 (died 695), does not include Sechnassach or his brother Cenn Fáelad

Cenn Fáelad

Cenn Fáelad mac Blathmaic followed his father Blathmac mac Áedo Sláine and his brother Sechnassach as High King of Ireland and king of Brega...

 (died 675) among its High Kings, the Chronicle of Ireland

Chronicle of Ireland

The Chronicle of Ireland is the modern name for a hypothesized collection of ecclesiastical annals recording events in Ireland from 432 to 911 AD....

, on which other Irish annals

Irish annals

A number of Irish annals were compiled up to and shortly after the end of Gaelic Ireland in the 17th century.Annals were originally a means by which monks determined the yearly chronology of feast days...

 were founded, named him as a High King on his death. The omission of Sechnassach and his brother Cenn Fáelad from this king list may be deliberate as it was compiled in the reign of Cenn Fáelad's killer Fínsnechta Fledach.

Sechnassach's marital alliances suggest that he had close relations with the kingdom of Leinster

Leinster

Leinster is one of the Provinces of Ireland situated in the east of Ireland. It comprises the ancient Kingdoms of Mide, Osraige and Leinster. Following the Norman invasion of Ireland, the historic fifths of Leinster and Mide gradually merged, mainly due to the impact of the Pale, which straddled...

. His only recorded marriage was with one Findelb ingen Chellaig, who may have been a daughter of Cellach Cualann

Cellach Cualann

Cellach Cualann mac Gerthidi was the last Uí Máil king of Leinster. Cellach's byname is derived from the land of Cualu which lay around Glendalough.The name Uí Máil may mean "grandsons of the princes"...

(died 715). His daughter, Bé Fáil (died 741), was in turned married to Cellach Cualann. Two other daughters of Sechnassach, Murgal and Mumain, are know, but no sons.

Little is recorded in the annals of Sechnassach's reign except his death. He was killed in November 671 by Dub Dúin, king of Cenél Coirpri, a minor Uí Néill kingdom on the upper reaches of the River Boyne

River Boyne

The River Boyne is a river in Leinster, Ireland, the course of which is about long. It rises at Trinity Well, Newbury Hall, near Carbury, County Kildare, and flows towards the Northeast through County Meath to reach the Irish Sea between Mornington, County Meath and Baltray, County Louth. Salmon...

 near Clonard

Clonard, County Meath

Clonard is a small village in County Meath, Ireland. It lies on the R148 regional road between the towns of Kinnegad and Enfield. This road was the main road between Dublin and Galway until the construction of the M4 motorway - it is still used by traffic avoiding the toll on the M4.It is notable...

. His brother Cenn Fáelad became High King after him, probably in 672.

The Annals of the Four Masters record of him:

Full of bridles and horsewhips, was the house in which dwelt Seachnasach,
Many were the leavings of plunder in the house in which dwelt the son of Blathmac.