The relic from Thomas Becket is going to be returned to England for the first time in 800 years in a week-long commemoration of the murdered archbishop.
The fragment of bone, believed to come from his arm, is currently held by the Basilica of Esztergom in Hungary.
The piece will travel from London, his birthplace, to Canterbury Cathedral, where he was murdered in 1170, as part of a seven-day 'pilgrimage'.
At each location senior clerics from the Anglican and Roman Catholic churches will conduct a series of special services .
Mr Becket's relic will be on display at a number of sites, including Westminster Cathedral, Westminster Abbey, the Houses of Parliament and Rochester and Canterbury Cathedrals.
The pilgrimage begins at Westminster Cathedral with a mass on Monday evening before moving to Westminster Abbey the next day.
Becket was the Archbishop of Canterbury from 1162 until he was murdered by knights of King Henry II in 1170.
The monarch reportedly said: "Who will rid me of this troublesome priest?"
He was killed in Canterbury Cathedral by four swordsmen in December 1170.
Becket was later canonised by Pope Alexander III and is thought of as a saint and a martyr in Catholic and Anglican denominations.
King Henry VIII ordered the destruction of the rest of Becket's bones and shrine when he dissolved the monasteries in 1538.
