Albert Barnes Commentary Judges 3:26

"And Ehud escaped while they tarried, and passed beyond the quarries, and escaped unto Seirah." — Judges 3:26 (ASV)

Seirath - “ The forest” or “weald,” which evidently bordered on the cultivated plain near Gilgal, and extended into “the mountain or hill country of Ephraim.” Once there, he was safe from pursuit (compare 1 Samuel 13:6), and quickly collected a strong force of Ephraimites and probably the bordering Benjamites.