Complex sentence: The walled town of Montgomery was attacked by the Welsh forces of Owain Glyndŵr in 1402 and sacked and burned, however the stone castle fortress held out against the attack though the garrison was not large the design and the men inside did their job.
Split into simpler sentences: The walled town of Montgomery was attacked by the Welsh forces of Owain Glyndŵr in 1402 and sacked and burned. Though the garrison was not large the design and the men inside did their job.