Alma 43:31 - 43:35
Alma 43: 31 Therefore, he divided his army and brought a part over into the valley, and concealed them on the east, and on the south of the hill Riplah;
Moroni now splits his forces. Part he stationed in the valley, concealing them on the east and south side of Riplah hill.
Alma 43: 32 And the remainder he concealed in the west valley, on the west of the river Sidon, and so down into the borders of the land Manti.
The rest he concealed on the west side of Sidon River near the borders of the land Manti.
Alma 43: 33 And thus having placed his army according to his desire, he was prepared to meet them.
Moroni now felt that he was prepared to surprise and defeat the Lamanites.
Alma 43: 34 And it came to pass that the Lamanites came up on the north of the hill, where a part of the army of Moroni was concealed.
The Lamanite army course came on the north side of hill Riplah, the hill where part of Moroni's forces were in hiding on the east and south sides.
Alma 43: 35 And as the Lamanites had passed the hill Riplah, and came into the valley, and began to cross the river Sidon, the army which was concealed on the south of the hill, which was led by a man whose name was Lehi, and he led his army forth and encircled the Lamanites about on the east in their rear.
So as the Lamanite began to enter the Sidon river south of hill Riplah, the Moroni's forces lead by a man named Lehi came out of concealment on the south and east sides of hill Riplah and took up positions at the rear and east sides of the Lamanite army. They were blocked from returning back the way they came.