Complex sentence: The city guard was called out, but the Abbey was stormed by a large mob, the Catholic furnishings placed there when it was restored as a chapel for James, torn down and the tombs of the Stuart kings desecrated.
Split into simpler sentences: The city guard was called out, but the Abbey was stormed by a large mob. The Catholic furnishings, placed there when it was restored as a chapel for James, were torn down and the tombs of the Stuart kings desecrated.