Complex sentence: Around 1770 the neoclassical architect Robert Adam designed Pulteney Bridge, using as the prototype for the three-arched bridge spanning the Avon an original, but unused, design by Palladio for the Rialto Bridge in Venice.
Split into simpler sentences: Around 1770 the neoclassical architect Robert Adam designed Pulteney Bridge, a three-arched bridge spanning the Avon. He used as his prototype an original, but unused, design by Palladio for the Rialto Bridge in Venice.