Complex sentence: At Robert's request, Philip I of Taranto brought reinforcements north and met with initial successes, but at the Battle of Montecatini, the combined forces of the Guelphs were defeated by Uguccione and the Ghibellines in a skirmish on the plain.
Split into simpler sentences: At Robert's request, Philip I of Taranto brought reinforcements and was successful. At the Battle of Montecatini, the combined forces of the Guelphs were defeated by Uguccione and the Ghibellines in a skirmish on the plain.