Complex sentence: For the remainder of the night, the division retired through the line held by the regiment until 04:00 on 1 April when the Wellington Mounted Rifles took over from the regiment, which then followed the division back to the river.
Split into simpler sentences: For the remainder of the night, the division retired through the line held by the regiment. Until 04:00 1 April when the Wellington Mounted Rifles took over from the regiment, which then followed the division back to the river.