Stained glass at Canterbury Cathedral is among the oldest in the world, a new study has found.
A group of windows at the city landmark may be the earliest surviving of their kind in the country and date back 891 years, according to a team of conservators and scientists from University College London (UCL).
A series of 86 windows depicting the Ancestors of Christ were installed at the Cathedral from the late 1170s through until 1220, periodically disrupted by political upheavals.
They were largely made in the late 12th century as part of a rebuilding programme which took place after a devastating fire tore through the building in 1174.
But the new UCL study has found several of the panels were actually created prior to the fire, meaning they would have been in place when Archbishop of Canterbury Thomas Becket was murdered at the Cathedral by followers of King Henry II in 1170.
The UCL group analysed the 86 windows using a non-destructive method of chemical analysis known as portable x-ray fluorescence, developed for the purpose by then-PhD student Laura Adlington.
The method allowed the glass to be analysed, without the need to remove physical samples from the windows.
The study's findings support a suggestion made by art historian Madeline Caviness in the 1980s that four of the panels installed in the 13th century are stylistically much older and date to the period 1130-1160 - meaning they could be up to 891 years old.
They had been present in the Quire of the earlier building and survived the fire when they were stored for future use and later adapted for the clerestory of the new building.
Léonie Seliger, director of the stained glass studio at Canterbury and a co-author of the study, says stained glass production began in about the 8th century.
"But the earliest existing stained glass windows in Europe are believed to date to the 1130s," she said.
"This study suggests that some of the Canterbury Ancestors may also date to this very early period.
"It also provides clues about the iconography of the early 12th-century church at Canterbury that was destroyed by fire.”
Dr Adlington described the new technique used in the study as "very exciting".
She said: “The inaccessibility of medieval stained glass, embedded in the walls of our cathedrals and churches, has limited our ability to learn more about them using scientific analysis.
"The potential of this in situ methodology using x-ray fluorescence to study medieval windows is very exciting.”
The new peer-reviewed study has been published in journal Heritage.
And a complete stained-glass window from Canterbury Cathedral has been loaned to the British Museum for a UK exhibition on Thomas Becket.
The window, which will be shown in it's original arrangement for the first time in 350 years, is one of the cathedral's greatest treasures and is currently on show at the British Museum in London.