Complex sentence: This began with the siege of Caerlaverock Castle in 1300, where after the failure of an initial assault, a small rock throwing engine was employed while three large engines (probably trebuchet, using a counter-weight mechanism), were constructed.
Split into simpler sentences: This began with the siege of Caerlaverock Castle in 1300. Here, after the failure of an initial assault, a small rock-throwing engine was employed, while three large engines (probably trebuchet, using a counter-weight mechanism), were constructed.