During their term of office, the two men led an expedition to the Julian Alps and secured the submission of several local peoples without fighting them.
This was apparently a follow-up to the campaign of the previous year's consuls against the Istrians.
In 218 BC, Catulus was member of a triumviral commission for the creation of the colonies of Placentia (Piacenza) and Cremona in Cisalpine Gaul.
The Second Punic War against Carthage had just broken out, and the commissioners were surprised by an uprising of the Gallic Boii and Insubres, caused by news that the Carthaginian general Hannibal was approaching.
Catulus and the others took refuge at Mutina (Modena), but were lured out and captured.