Complex sentence: In the 1720s Giacomo Leoni, an architect from Venice, extensively re-modelled the house, giving it a courtyard plan and, while retaining some of its Elizabethan features, making major additions in a Palladian style with Baroque features.
Split into simpler sentences: In the 1720s Giacomo Leoni, an architect from Venice, made extensive additions to the house, creating a courtyard plan. While he retained some of its Elizabethan features, he made major additions in a Palladian style with Baroque features.