Complex sentence: With Spanish Dominion, Vasto became fief of the Marquises of d'Avalos who contributed to the Palazzo's present-day structure; in the reign of Cesare Michelangelo (marquis from 1697 to 1729), Vasto reached its zenith.
Split into simpler sentences: With Spanish Dominion, Vasto became fief of the Marquises of d'Avalos. Theirs is the contribution to the building's present-day structure; in the reign of Cesare Michelangelo (marquis from 1697 to 1729), Vasto reached its zenith.