Some of the stained glass at Canterbury Cathedral may have been in place when St Thomas Becket was murdered.
The panels, depicting the Ancestors of Christ, have been re-dated using a new, non-destructive technique.
And the analysis indicates that some of them may date back to the mid-1100s.
The windows would therefore have been in place when the Archbishop of Canterbury, Thomas Becket, was killed at the cathedral in 1170.
Léonie Seliger, the head of stained glass conservation at the cathedral, told BBC News the stained glass "would have witnessed the murder of Thomas Becket".
She said, "They would have witnessed Henry II come on his knees begging for forgiveness.
"They would have witnessed the conflagration of the fire that devoured the cathedral in 1174. And then they would have witnessed all of British history."
Thomas Becket was murdered in the cathedral by four knights who believed they were acting on the orders of Henry II.