John Gill Commentary Judges 9:34

"And Abimelech rose up, and all the people that were with him, by night, and they laid wait against Shechem in four companies." — Judges 9:34 (ASV)

And Abimelech rose up, and all the people that were with him,
by night

According to the advice of Zebul:

and they laid wait against Shechem in four companies ;

he divided his army into four parts, which he placed on the four sides of the city, at some distance from it, to act as they should have opportunity, to find ways and means of getting into it on either quarter.