What is St Patrick's Day? All you need to know about Ireland's favourite holiday

Ever year on March 17, millions around the world with a skerrick of Irish lineage - and even those without - celebrate St Patrick's Day. St Patrick was a 5th-century Romano-British Christian missionary, who was born in Britain in AD 387.  When he was 16, he was kidnapped by Irish raiders and taken as a slave to Ireland. While among the sheep, he supposedly "found God". In his 30s he returned to Ireland, to convert the pagan Irish to Christianity, supposedly using the three leaves of a shamrock to explain the Christian holy trinity: the Father, the Son, and the Holy Spirit. While legend credits St Patrick's evangelising with converting the Irish to Christianity, historians believe there were already Christian believers in Ireland by the time Patrick arrived.