Albert Barnes Commentary 1 Samuel 22:1

"David therefore departed thence, and escaped to the cave of Adullam: and when his brethren and all his father`s house heard it, they went down thither to him." — 1 Samuel 22:1 (ASV)

To the cave Adullam. This should be understood as the cave “of” Adullam, located near the town of that name. Adullam was a town in the Shephelah region of Judah, not far from Bethlehem and at a lower elevation. Innumerable caverns, one nearly 100 feet long, are excavated in the soft limestone hills in the neighborhood of Beit-Jibrin. (The cave is placed by Ganneau and Conder on the 500-foot-high hill over ‘Aid el Ma or Miyeh.)

David’s brothers and relatives joined him there, partly out of sympathy for him and partly because their own lives were in jeopardy from Saul’s furious enmity.