Complex sentence: Initially, only agricultural improvements were carried out; then in 1485, work started began on the villa itself, to designs by Giuliano da Sangallo, who created a large fortified, quadrangular country house built around a central courtyard.
Split into simpler sentences: Initially, only agricultural improvements were carried out; then in 1485, work started began on the villa itself, to designs by Giuliano da Sangallo. A large fortified, quadrangular country house built around a central courtyard.