Complex sentence: Pitti's prosperity declined from 1464, following the death of Cosimo, his patron, he died in 1472, work on his grand palazzo had stopped in 1465, and he was not to see it completed.
Split into simpler sentences: Pitti's prosperity declined from 1464, following the death of Cosimo, his patron. Pitti died in 1472, work on his grand palazzo had stopped in 1465, and he was not to see it completed.