Complex sentence: Catania had largely recovered from the damage caused by the earthquake of 1693, largely due to the efforts of the city architect Giovanni Battista Vaccarini, who had rebuilt vast tracts of the city in Baroque style, such as the area around the Cathedral.
Split into simpler sentences: Catania had largely recovered fro the damage caused by the earthquake of 1693, largely due to the efforts of the city architect Giovanni Battista Vaccarini. Who had rebuilt in Baroque style, vast tracts of the city including the area around the Cathedral.