It’s not very big. Maybe twelve inches in diameter. But the little round window set high in the wall of St Peter’s Church, Jarrow, is the oldest stained-glass window in the world.

It’s on the right-hand side of the chancel. Looking up, you can see three deeply recessed windows. These window openings are all original; they were made when the church was completed in 685 (there’s a larger window but that’s a later addition).

To build and furnish his new churches the man who commissioned them, Benedict Biscop, imported stone masons and glaziers from Europe as both skills were unknown to the Anglo-Saxons. Benedict was an indefatigable traveller: he made five trips to Rome, plus various other excursions during his life. The churches he built – St Peter’s in Wearmouth and St Paul’s in Jarrow – were the first stone buildings since the departure of the Romans and the first with glass windows.

The original glass was long gone when Rosemary Cramp began excavating at Jarrow in 1963 (the excavations went on until 1978). But during these excavations, Cramp and her team found many small pieces of glass that date from the time the monastery was built. So when the dig was finished, these fragments of glass were put back in place, in the window for which they had first been made, 1300 years ago.

I should think those anonymous glassmakers would be astonished, but not a little pleased, to learn that their glass still lets the light into the church they crossed the sea to work on.