Complex sentence: Side chapels were added in the north aisle in the 14th century and in the south aisle in the 15th and the 16th, one of the latter (15th) is especially rich in decorations.
Split into simpler sentences: Side chapels were added in the north aisle in the 14th century and in the south aisle in the 15th and the 16th centuries. One of the latter (15th) is especially rich in decorations.