Complex sentence: Only Gaeta, Messina, and Civitella del Tronto still held out, and the siege of the former by the Piedmontese began on November 6,1860.
Split into simpler sentences: Only Gaeta, Messina, and Civitella del Tronto still held out. The Siege of Gaeta by the Piedmontese began on November 6,1860.