Norsemen sailed up the Shannon in 812, pillaged the existing settlement and burned the monastery at Mungret. By 922 they had returned permanently. A Viking jarl named Thórir Helgason - Tomrair mac Ailchi in Irish records - was using the Limerick fleet to raid up the river as far as Lough Ree. For about a century, Limerick rivalled Dublin as the dominant Norse base in Ireland. The two cities fought, made alliances, and split prizes. The last Norse King of Limerick was Ivar, defeated and killed by Brian Boru's brother Mathgamain mac Cennétig in the 960s; Brian Boru himself made Limerick a centre of his Munster kingdom shortly after. Then came the Normans. King John of England ordered a great castle built on King's Island around 1200; it still stands. Under Norman peace the medieval city grew - English Town on the island, Irish Town on the south bank, both eventually walled, both eventually one city.

In 1642 Irish Confederate forces under Garret Barry captured King John's Castle from its small English garrison. In 1651, after the Battle of Worcester, Cromwell's son-in-law Henry Ireton arrived with the New Model Army and laid siege to Limerick for twelve brutal months. Famine and plague killed an estimated 5,000 people inside the walls before the city surrendered in October 1651. Forty years later came the worst of the three. After the Williamite victory at the Boyne in 1690, 14,000 French and Irish Jacobite troops retreated to Limerick. Patrick Sarsfield's spectacular night raid destroyed the Williamite siege train at Ballyneety, and the first siege was driven off. The second, in 1691, was different. The promised French reinforcements failed to arrive; 850 defenders were massacred on Thomond Bridge; the city sued for peace. On 3 October 1691 the Treaty of Limerick was signed - reportedly, using a large stone as a table on the bridge. The Treaty allowed the Catholic Jacobites to leave with full military honours for France. Sarsfield sailed with 19,000 troops - the Flight of the Wild Geese - and formed the Irish Brigade in French service. Two days later, French reinforcements finally arrived. Sarsfield refused to break his word. The English Parliament repudiated the Treaty within two years. Limerick has called itself the City of the Broken Treaty ever since.

The eighteenth century brought, paradoxically, prosperity. Penal Laws restricted Catholic life, but Limerick's role as Ireland's main western port for transatlantic trade made the Protestant gentry and Catholic merchant class both rich. The town doubled, then doubled again. In 1765 Edmund Sexton Pery commissioned the Italian engineer Davis Ducart to design a new town on his land south of the medieval city. The result, Newtown Pery, gave Limerick the long terraced Georgian streets - O'Connell Street, Patrick Street, Rutland Street, the Crescent, Pery Square - that still define the city centre. Then came the Famine. Limerick's wealth, like Ireland's, depended on agricultural exports; the merchant Francis Spaight recorded 386,909 barrels of oats and 46,288 barrels of wheat shipped from Limerick between June 1846 and May 1847, a year of catastrophic potato failure. Spaight told a parliamentary committee that he found 'the failure of the potato crop to be the greatest possible value in one respect, in enabling us to carry out the emigration system.' The famine emptied the countryside. In 1904, the city's small Jewish community - mostly Lithuanian refugees from earlier persecution - was subjected to a sustained, two-year economic boycott led by a Redemptorist priest, Father John Creagh. Many Jewish families left for Cork, where they were welcomed. One of their grandchildren, Gerald Goldberg, became Lord Mayor of Cork in 1977.

April 1919 saw the Limerick Soviet - a fortnight-long general strike against British military occupation, in which the Limerick Trades Council printed its own money and controlled food prices for the duration. Two years later, on 6 March 1921, three Black and Tans assassinated Mayor George Clancy and his wife in their home; the previous mayor, Michael O'Callaghan, was killed the same night. These Curfew Murders remain one of the bitterest local memories of the War of Independence. In July 1922, during the Civil War, Free State troops shelled and stormed the Castle Barracks and Ordnance Barracks; six Free State soldiers and twelve civilians died in the fighting. The infant Free State then built the Shannon Hydroelectric Scheme - the great Ardnacrusha power station, built by Siemens between 1925 and 1929 - which electrified rural Ireland and pulled Limerick into the modern era. The Emergency Powers Act of 1939 kept Ireland neutral through the Second World War; an army of 300,000 was raised to deter invasion from either side. Shannon Airport, built on bogland in 1942, opened the transatlantic era. By the 1960s, Shannon was where Che Guevara, marooned by a mechanical fault on a Cuban flight in 1965, drank in a Limerick hotel and turned up at the airport wearing a sprig of shamrock for St Patrick's Day.

Post-war Limerick was characterised by emigration and unemployment. Frank McCourt's Angela's Ashes - the Pulitzer-winning memoir of a 1930s and 40s Limerick childhood - documented the poverty that drove so many of his generation abroad. Richard Harris, the actor, and Terry Wogan, the broadcaster, both left as young men and never moved back. From the 1990s the Celtic Tiger economy reversed the flow. Limerick became a centre of multinational investment - Johnson & Johnson's Vistakon in Castletroy; Regeneron and Eli Lilly in Raheen; Verizon, Microsoft, Google operations across the city. The 2008 financial crisis hit hard: house prices halved and took a decade to recover. By the 2020s the recovery was real but uneven. The University of Limerick, founded in 1972 as the NIHE and granted full university status in 1989, has grown into a research institution of 16,000 students. Riverpoint - Ireland's third-tallest building at 58 metres - opened in 2008, looking down at the same Shannon the Vikings sailed up twelve centuries earlier. The city's first mosque is near the Crescent Shopping Centre. The river goes on.