Complex sentence: This is a huge fresco representing an Allegory of Divine Providence and Barberini Power, begun in 1633 and completed in 1639; a sketch for it is now exhibited with it, but its authenticity is open to doubt.
Split into simpler sentences: This is a huge fresco representing an "Allegory of Divine Providence and Barberini Power", begun in 1633 and completed in 1639. A sketch for it is now exhibited with it, but its authenticity is open to doubt.