Complex sentence: The building of Rosewell was begun in 1725 by Mann Page I (1691--1730), who married in 1718 Judith Carter, the daughter of Robert "King" Carter.
Split into simpler sentences: The building of Rosewell was begun in 1725 by Mann Page I (1691--1730). In 1718 he had married Judith Carter, the daughter of Robert "King" Carter.