Here's a mystery: a fine Norman doorway set in what is obviously a later window arch.
The solution is that St Denys in York was once a much larger church. Its website explains:
The church was founded before 1154, on the site of a late Saxon church and an earlier Roman building. A Roman altar and an Anglo-Danish ‘hogsback’ tombstone were found on the site in 1846. Traces of these earlier buildings came to light during trial excavations in 2001 to investigate the church’s foundations (which proved extremely stable).
The present building dates mainly from the 14th and 15th centuries, but has been much reduced from its original size, due to a series of a historical mishaps – the former spire was damaged by Civil War cannon fire and then struck by lightning, and the transepts and long nave were demolished in 1797.
So what survives now is only the east end with its flanking chapels, making an unusually square-shaped church entered through a fine Norman doorway (from the demolished nave), set in what was originally the site of a window.The result of this troubled history is that, unusually, the church is wider than it is long. I couldn't help thinking how good it would be for a political meeting. Even a few people would make it look respectably full, but you could cram many more in if you had to.
Legend has it that Henry Percy, Third Earl of Northumberland, who fell in the Battle of Towton - the "largest and bloodiest battle ever fought on English soil" - in 1461 was buried here.