“The Lamanites Began to Cross the River Sidon”

The Lamanite army has entered the valley and must cross the river to reach Manti (and later Zarahemla). By waiting until the Lamanites actually begin to cross the river (which would certainly hamper their mobility), Moroni assures the maximum effectiveness of his two-pronged attack.

I speculate that this Lehi₃ is the same as Zoram₂’s son, whom we first met in Alma 16:4–5.