Luimneach originally referred to the general area along the banks of the Shannon Estuary known as Loch Luimnigh. Luimneach meaning flat area and the description is accurate as the land consists mostly of a fertile limestone plain. Moreover, the county of Limerick is ringed by mountains. The highest point in the county is located in its south-east corner at Galtymore (919 m), which separates Limerick from County Tipperary. The county is not a simply a plain, its topography consists of hills and ridges. The eastern part of the county is part of the Golden Vale, which is well known for dairy produce and consists of rolling low hills. This gives way to very flat land around the centre of the county, with the exception being Knockfierna at 288 m high. Towards the west, the Mullaghareirk Mountains (Mullach an Radhairc in Irish, roughly meaning "mountains of the view") push across the county offering extensive views east over the county and west into County Kerry.
The earliest settlement in the city, Inis Sibhtonn, was the original name for King's Island during the pre-Viking and Viking eras. This island was also called Inis an Ghaill Duibh, "The Dark-(haired) Foreigner's Island". The name is recorded in Viking sources as Hlymrekr.
The city dates from 812 which is the earliest probable settlement; however, history suggests the presence of earlier settlements in the area surrounding King's Island, the island at the historical city centre. Antiquity's map-maker, Ptolemy, produced in 150 the earliest map of Ireland, showing a place called "Regia" at the same site as King's Island. History also records an important battle involving Cormac mac Airt in 221 and a visit by St. Patrick in 434 to baptise an Eóganachta king, Carthann the Fair. Saint Munchin, the first bishop of Limerick died in 652, indicating the city was a place of some note. In 812 the Vikings sailed up the Shannon and pillaged the city, burned the monastery of Mungret but were forced to flee when the Irish attacked and killed many of their number. The Normans re-designed the city in the 12th century and added much of the most notable architecture, such as King John's Castle and St Mary's Cathedral.
William Camden wrote that the Irish had been zealous about their antiquity since the deluge and were ambitious to memorialise important events for posterity. The earliest provable settlement dates from 812 according John Ferrar's History of Limerick from 1787.
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However, history suggests the presence of earlier settlements in the area surrounding King's Island, the island at the historical city centre. Antiquity's map-maker, Ptolemy, produced in 150 AD the earliest map of Ireland, showing a place called "Regia" at the same site as King's Island. History also records an important battle involving Cormac mac Airt in 221 and a visit by St. Patrick in 434 to baptise a Eóganachta king, Carthann the Fair. Saint Munchin, the first bishop of Limerick died in 652, indicating the city was a place of some note. In 812 Danes sailed up the Shannon and pillaged the town, burned the monastery of Mungret but were forced to flee when the Irish attacked and killed many of their number.
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.
In early medieval times Limerick was at the centre of the Kingdom of Thomond which corresponds to the present day Mid West Region however, the Kingdom also included North Kerry and parts of South Offaly. One of the kingdom's most notable kings was Brian Boru, ancestor of the O'Brien Clan of Dalcassians. The word Thomond is synonymous with the region and is retained in place names such as Thomondgate, Thomond Bridge & Thomond Park.
Limerick in the sixteenth and seventeenth centuries was often called the most beautiful city in Ireland. The English-born judge Luke Gernon, a resident of Limerick, wrote in 1620 that at his first sight of the city he had been amazed at its magnificence: "lofty buildings of marble, like the Colleges in Oxford".
During the civil wars of the 17th century the city played a pivotal role, besieged by Oliver Cromwell in 1651 and twice by the Williamites in the 1690s.
The Treaty of Limerick ended the Williamite war in Ireland which was fought between supporters of the Catholic King James II (Jacobites) and the Protestant King William of Orange (Williamites). The treaty offered toleration to Catholicism and full legal rights to Catholics that swore an oath of loyalty to William and Mary. The Treaty was of national significance as it ensured closer British and Protestant dominance over Ireland. The articles of the Treaty protecting Catholic rights were not passed by the Protestant Irish Parliament which rather updated the Penal Laws against Catholics which had major implications for Irish history. Reputedly the Treaty was signed on the Treaty Stone, an irregular block of limestone which once served as a mounting block for horses. This stone is now displayed on a pedestal at Clancy Strand. Because of the treaty, Limerick is sometimes known as the Treaty City. This turbulent period earned the city its motto: Urbs antiqua fuit studisque asperrima belli (An ancient city well studied in the arts of war).
The peace times that followed the turmoil of the late 17th Century allowed the city to prosper through trade in the late 18th century. During this time Limerick Port established itself as one of Ireland's major commercial ports exporting agricultural produce from one of Ireland's most fertile areas, the Golden Vale, to Britain and America. This increase in trade and wealth, particularly amongst the city's merchant classes saw a rapid expansion of the city as Georgian Limerick began to take shape. This gave the city its present-day look including the extensive terraced streets of fine Georgian townhouses which remain in the city centre today. The Waterford and Limerick Railway linked the city to the Dublin–Cork railway line in 1848 and to Waterford in 1853. The opening of a number of secondary railways in the subsequent decades developed Limerick as a regional centre of communications. However, the economic downturn in the European conflicts of the French Revolution and Napoleonic eras, and following the Act of Union 1800, and the impact of the Great Irish Famine of 1848 caused much of the 19th Century to be a more troubled period.
The Limerick boycott was an economic boycott waged against the small Jewish community for over two years in the first decade of the twentieth century. It was accompanied by a number of assaults, stone throwing and intimidation, which caused many Jews to leave the city. It was instigated in 1904 by a Redemptorist priest, Father John Creagh.
During the Irish War of Independence, the Limerick Soviet was a self-declared soviet that existed from 15 to 27 April 1919. A general strike was organised by the Limerick Trades and Labour Council, as a protest against the British Army's declaration of a "Special Military Area" under the Defence of the Realm Act, which covered most of Limerick city and a part of the county. During the strike a special strike committee was set up to print their own money, control food prices and publish newspapers.
By the mid-20th century, Limerick was characterised by economic stagnation and decline as many traditional industries closed or left the city. However, there were some success stories. In 1942 Shannon Airport (located 20 km west of the city) opened for the first time offering transatlantic flights. In 1959, Shannon Airport enabled the opening of the Shannon Free Zone which attracted a large number of multinational companies to the region. A long campaign for a third level educational institute to be located in the city finally bore fruit with the establishment of NIHE Limerick in 1969 which eventually became the University of Limerick in 1989.