At the outset of the war, the Vietnamese king ordered a large army to cross into Muang Phuan and from there to attack Lan Xang in fall 1479. Estimates of the tactics used by the Vietnamese vary from a single wave of three columns to a single wave of five columns to multiple waves of an amassed force. As the Vietnamese advanced, the Lao army formed and marched to confront the invaders. The two armies first met on the Plain of Jars in Muang Phuan where a battle was fought for several days. Estimates of the number of men in the armies were as large as 200,000 men on a side. Historians believe, however, that such estimates were “grossly exaggerated.”.