Complex sentence: During the English occupation of Scotland under the Commonwealth, fortresses in the style of the trace italienne were built, polygonal in plan with triangular bastions at Ayr, Inverness and Leith.
Split into simpler sentences: During the English occupation of Scotland under the Commonwealth, fortresses in the style of the trace italienne were built. These were polygonal in plan with triangular bastions, as at Ayr, Inverness and Leith.