Nearly four months were spent by Louis in a vain attempt to take this place; his supplies were cut off by the sailors of the Cinque Ports, who were in John's interest; and though Louis's father sent him a battering machine, called Malvoisine, or "Bad Neighbor," he could make no impression on the walls.

Picard's plan was to connect two points by a series of triangles, and, thus ascertaining the length of the arc of a meridian intercepted between them, to compare it with the difference of latitudes found from celestial observations. The stations were Malvoisine in the vicinity of Paris, and Sourdon near Amiens.