the plan for 1677 was to take valenciennes, cambrai and saint-omer, completing the french "frontière de fer" or 'iron border;' louis calculated this would leave the dutch little reason to continue. supply depots were assembled along the border with the spanish netherlands, enabling operations to begin in february, a month earlier than usual. in late february, a detachment of 12,000 moved against saint omer, while the main army of 35,000 under luxembourg besieged valenciennes.