The Battle of the Trebia occurred on the left bank of the Trebbia River.
The border with the Province of Pavia in southernmost Lombardy follows the Trebbia for about 2,000 m (6,600 ft) where it bends around Ponte Organasco, so that some of the river and bottom lands are in Lombardy
 It widens and merges with the Pianura Padana, "plain of the Po", beyond Rivergaro and a few miles later encounters the suburban communities on the west side of Piacenza before entering the Po

