025 colosseo in 4 foto

1. Overall image for context (not photoshopped)

2. Brick wall introduced (unknown date), presumably
to stabilize the end condition of the wall and prevent collapse.
This type of intervention is not en vogue among preservationists
and conservationists today. Pros: structural stability,
life safety, easy to distinguish that this is not original,
clearly marked with date of intervention on placards.
Cons: does not retain monument in original form,
is not a reversible intervention, does not adhere to
"minimal intervention" policy and is a severe change
to substructure and foundation system. (The foundation of
the Colosseum consists of at least one more layer of arched
walls subgrade.)

3. End bay - this arch is obviously collapsing. Without the
intervention of the brick wall as backup, this portion of
the wall would surely have collapsed.

4. Close up view of the cracking and displacement
of the masonry. I don't know how the stones have been
attached to the newer brick wall. One of the important
precepts of preservation/conservation is to use compatible
materials in both chemical compatibility and mechanical
(displacement) compatibility. (If I have some time, I could
get the answer in the library here of course!)