Complex sentence: Ferniehirst Castle (sometimes spelt Ferniehurst) was built around 1470 to hold the gate for Scotland and to serve as a base for military raids and cattle-lifting forays.
Split into simpler sentences: Ferniehirst Castle (sometimes spelt Ferniehurst) was built around 1470. It was built to hold the gate for Scotland and to serve as a base for military raids and cattle-lifting forays.