They = Christians in general, not a monk in particular. After the proclamation of Christianity as the official religion of the empire, it took only a few years

They = Christians in general, not a monk in particular. After the proclamation of Christianity as the official religion of the empire, it took only a few years/decades before Christians were on a full-blown iconoclastic campaign of destruction of so-called "pagan" religion, and all non-Christian culture in general. This meant murder and forced conversions, but also destruction of patrimony: libraries burned, temples razed, schools closed, statues smashed, etc.