Thousands of years of history at a remote priory in Norfolk could be unearthed after the discovery of giant medieval graffiti on its walls.
The Norfolk Medieval Graffiti Survey (NMGS) group claims to have found 8ft (2.4m) building plans etched into the stonework of Binham Priory, near Wells.
The drawings, which are too faint to photograph, seem to show how the building's west front was built.
"It was difficult to believe what I was seeing," said NMGS's Matthew Champion.
"Most graffiti inscriptions tend to be relatively small and modest. This was just so big that it wasn't really possible to see exactly what it was until we had surveyed the whole wall surface.
"It was only after we had carried out the measured survey that we realised it related to the west front.
"Large parts of the inscription are still impossible to see as they are beneath large fragments of a surviving 14th Century paint scheme. There's an awful lot more there that we simply can't get at."
According to Mr Champion, the findings mark the earliest sketches of window's bar tracery design to be found anywhere in England.
The survey at the Gothic priory should continue for the next few months, where photocomposition will reveal the true extent of the inscriptions.
"If these inscriptions do all relate to the west front then they may hold the key to exactly what the master mason truly envisaged when work began here in the early 13th Century."
Much of the west front of Binham Priory has been bricked-up since the end of the 18th Century due to the collapse of the west window.