Complex sentence: Following floods in the mid seventeenth century, when the River Wye changed course, the old church (now south of the river) fell into disrepair and a new one was built still further south in 1661, though the current building dates from 1837.
Split into simpler sentences: Following floods in the mid seventeenth century, the River Wye changed course and the old church found itself south of the river and subsequently fell into disrepair. A new one was built still further south in 1661, though the current building dates from 1837.