Complex sentence: Leopoldo Pollack (1751, Vienna--1806, Milan) was an Austrian-born Italian architect who was active in Milan where he became one of the leading proponents of Neoclassical architecture.
Split into simpler sentences: Leopoldo Pollack (1751, Vienna--1806, Milan) was an Austrian-born Italian architect who was active in Milan. He was one of the leading proponents of Neoclassical architecture.