Complex sentence: Since then the cathedral has undergone a number of renovations and some alterations: belfries were added in the latter half of the 17th century and in 1868 a sacristy was constructed at the cathedral's east end.
Split into simpler sentences: Since then the cathedral has undergone a number of renovations. Belfries were added in the latter half of the 17th century and in 1868 a sacristy was constructed at the cathedral's east end.