Complex sentence: The poet Petrarch wrote letters to Simon Boccanegra and to the doge of Venice humanist appealing to them to end their fratricidal wars and find a common aim.
Split into simpler sentences: The poet Petrarch wrote two letters written to Simon Boccanegra, and to the doge of Venice. In these letters the humanist appealed to them to end their fratricidal wars and find a common aim.