This thread is dedicated to all the damages done by the iconoclasm and the destructive rage that early Christians developped against all that was pagan and polytheistic.
It was something that destroyed, I guess the 80% of the cultural heritage of that time, if we think of statues, temples, shrines.
1. The most fulgid example was the temple of Artemis in Ephesus. Ephesus was one of the very first Christian communities and had this magnificent temple, with high columns. It was destroyed by the Eastern Roman Empire, which enabled a zero tolerance towards Paganism, in the V century.
This is the before and after:
People seem to assume everything that no longer exists must have been "destroyed". The opposite is more true, most ancient things that exist have been specifically saved in one way or the other. The default is for things to no longer exist.
We can see the exact same process in every Western country today when we look at the closure and sometimes repurposing of Churches.
It would make little sense to paint this as the 'destruction' of churches by non-Christians, as it is just the social and economic reality of the decline in numbers of people attending church. The same thing happened in the past, pagan temples that were not being used were not economically viable and fell into disrepair. Often their stone would be repurposed to build city walls, houses or churches as it was a valuable resource.
Even in the 18th C, much of Hadrian's Wall was used to build roads to improve logistics and help defeat the Jacobite Uprising. We find this awful today, but people back then had different priorities and you can't really blame them.
We might like to think of ancient people spending lots of money preserving buildings and treasures for the benefit of modern tourists and aesthetes, but we save what we value and allow the decline of that which we do not. We can't expect all societies throughout history to have the same preferences as we do.
Throughout history people have valued some things for their historical value, but a lot for the drive to preserve "cultural heritage" in general is a more modern thing.
Some pagan temples were destroyed (mostly in a small number of locations like Syria), although the phenomenon is massively overstated, and the vast majority of pagan buildings and artefacts just died a natural death, like many Churches are doing today as there are no benefactors to pay for their preservation.