Dublin celebrated its 'official' millennium in 1988, meaning the Irish government recognised 988 as the year in which the city was settled and that this first settlement would later become the city of Dublin. It is now thought the Viking settlement of about 841 was preceded by a Christian ecclesiastical settlement known as ''Duibhlinn'', from which ''Dyflin'' took its name. Beginning in the 9th and 10th century, there were two settlements which later became the modern Dublin. The subsequent Scandinavian settlement centred on the River Poddle, a tributary of the Liffey in an area now known as Wood Quay. The Dubhlinn was a pool on the lowest stretch of the Poddle, where ships used to moor. This pool was finally fully infilled during the early 18th century, as the city grew. The Dubhlinn lay where the Castle Garden is now located, opposite the Chester Beatty Library within Dublin Castle. ''Táin Bó Cuailgne'' ("The Cattle Raid of Cooley") refers to ''Dublind rissa ratter Áth Cliath'', meaning "Dublin, which is called Ath Cliath".