The earliest record of vikings at Limerick is in 845, reported by the Annals of Ulster, and there are intermittent reports of vikings in the region later in the 9th century. Permanent settlement on the site of modern Limerick had begun by 922. In that year a Viking jarl or prince called Tomrair mac Ailchi—Thórir Helgason—led the Limerick fleet on raids along the River Shannon, from the lake of Lough Derg to the lake of Lough Ree, pillaging ecclesiastical settlements. Two years later, the Dublin vikings led by Gofraid ua Ímair attacked Limerick, but were driven off. The war between Dublin and Limerick continued until 937 when the Dubliners, now led by Gofraid’s son Amlaíb, captured Limerick’s king Amlaíb Cenncairech and for some reason destroyed his fleet. However, no battle is actually recorded and so a traditional interpretation has been that Amlaíb mac Gofraid was actually recruiting Amlaíb of Limerick for his upcoming conflict with Athelstan of England, which would turn out be the famous Battle of Brunanburh. The 920s and 930s are regarded as the height of Norse power in Ireland and only Limerick rivalled Dublin during this time.
The last Norse king of Limerick was Ivar of Limerick, who features prominently as an enemy of Mathgamain mac Cennétig and later his famous brother Brian Boru in the Cogad Gáedel re Gallaib. He and his allies were defeated by the Dál gCais, and after slaying Ivar Brian would annexe Norse Limerick and begin to make it the new capital of his kingdom. The power of the Norsemen never recovered, and they reduced to the level of a minor clan; however, they often played pivotal parts in the endless power struggles of the next few centuries.
Brian Boru’s son, Donough, was routed by Diarmait mac Maíl na mBó in the year 1058 when Limerick was burned, a punishment he repeated five years later. A year later Diarmait beat Donough again forcing him to flee overseas and installing Turlough instead. Obviously Limerick was of great importance as evidenced by being a contentious issue between neighbouring chieftains and foreigners who burned and pillaged the city. Brian Boru’s sons were usually called Kings of north Munster though their reigns were rather disturbed until 1164 when Donnchad mac Briain became King of Munster. His reign was successful, founding monasteries and nunneries, constructing several monuments, including a church on the Rock of Cashel, and in his grant bestowing his Limerick Gothic palace to the church he styled himself King of Limerick. However the Danes were still a powerful force who were able to obtain four sequential Danish bishops concentrated by the Archbishop of Canterbury not subservient to the See of Cashel.
The arrival of the Normans to the area in 1173 changed everything. Domnall Mór Ua Briain, the last styled King of Limerick, burned the City to the ground in 1174 in a bid to keep it from the hands of the new invaders. After he died in 1194, the Normans finally captured the area in 1195, under the leadership of Prince John. In 1197, King Richard I of England granted the city its first charter, and its first Mayor, Adam Sarvant, ten years before London. A castle, built on the orders of King John and bearing his name, was completed around 1200. Under the general peace imposed by Norman rule, Limerick prospered as a port and trading centre. By this time the city was divided into an area which became known as “English Town” on King’s Island surrounded by high walls, while another settlement, named “Irish Town”, where the Irish and Danes lived, had grown on the south bank of the river. In 1216 King John further granted the areas North (as far as a tributary of the Shannon) and South of the River to City to be known as the “Northern” and “Southern” Liberties. Around 1395 construction started on walls around Irishtown that were not completed until the end of the 15th century.
Limerick is stronger and more beautiful than all the other cities of Ireland, well walled with stout walls of hewn marble…there is no entrance except by stone bridges, one of the two of which has 14 arches, and the other eight … for the most part the houses are of square stone of black marble and built in the form of towers and fortresses.
Luke Gernon, an English-born judge and resident of Limerick, wrote a similar description in 1620:
In the 15th and 16th centuries, Limerick became a city-state isolated from the principal area of effective English rule -the Pale. Nevertheless, the Crown remained in control throughout the succeeding centuries. During the Reformation tensions arose between those loyal to the Catholic Church and those loyal to the newly established state religion — the Church of Ireland.