Complex sentence: Most of the remaining defenders retired to Château Maltot on the far side of the road and were cut off and as the 4th Wilts moved forward to the Rau de Maltot stream, they were stopped by fire from the château.
Split into simpler sentences: Most of the surviving defenders retired to Château Maltot on the far side of the road and were cut off. As the 4th Wilts moved forward to the Rau de Maltot stream, they were stopped by fire from the château.