Its centre was the ancient and walled city of Piacenza (Latin Placentia) at the confluence of the Trebbia and the Po, just downriver from the royal capital of Pavia.
[1] On 3 June 870, the Emperor Louis II granted his queen, Engelberga, the monastery of San Pietro in the county of Piacenza along with seven manors to support the convent of San Sisto she had recently founded within the walls of Piacenza.
In 874, Louis extended granted her control of the aqueduct system in the county, as well as the right to certain building materials and to a canal.
[2] The old and wealthy abbey of Bobbio lay within the county of Piacenza, and its abbots were in frequent conflict with the counts.
In 929, a great trial was held in Pavia of several Piacentine noblemen accused of usurping Bobbio's lands.