How's about this?
So this is the Arenes at Nimes in the Languedoc, one of the biggest Roman amphitheatres that still survives. (Okay, it's smaller than the Colosseum, but, eh, most things are). You may not think you know what amphitheatres look like, but you do - they're oval, with range upon range of arches leading in.
These arches were entrances on the ground floor and then ventilation higher up. The crowd control for getting thousands of people in was quite sophisticated and there was lots of roomy corridor space too, it's not just an outer shell. This is a fancy amphitheatre, so there's decoration like pilasters between the arches. Very smart. But why's there a blocked arch? Why is there a mean little window in it?
That's because the Arenes had an afterlife. Roman amphitheatres pretty much stopped being used for the games 4th-5th cent CE, but they were still big impressive buildings near the centre of cities, where those cities survived the fall of Rome. Often they were used as stone quarries for people living nearby - all those lovely dressed stone blocks, so handy. But in Nimes, the population took the opposite view: they moved *in* to the Arenes, because it was defensible and handy. Townspeople, and the lay power for the area, represented by a garrison - who became known as the Knights of the Arena. If that's not a name for history, I don't know what is.
A bit draughty with all those arches, of course, so over time, they were blocked up. And medieval people still needed a bit of light, so that's a medieval twin-arched window inset. It wasn't just medieval people. The Arenes was inhabited right up to the 18th century - it was a town, really, with two churches, and people owning an arch or two for themselves, and buildings all over what had been the central arena space. There are quite modern-looking surviving plans of property ownership, Old Madame So-and-so in the upper tiers. But eventually, antiquaries and people who love *older* history got hold of it, and the Arenes was cleared of all those modern encroachments, so that it looked classical and right for tourists and the glory of Nimes. (12th century modern, that kind of deal.) So now it looks roughly as it would have in 400CE
Just two arches were left blocked as a reminder of the 1300 years between the Roman amphitheatre and the tourist relic. I know this because I listened to the whole very long and informative audioguide for touring the Arenes, and then walked round the entire building to find this vestige. I like my history thorough!