John Gill

Now, when Jesus had heard that John was cast into prison,.... John was cast into prison by Herod; the reason of it may be seen in Mat 14:3. The prison into which he was cast, according to Josephus (s), was the castle of Machaeras: here he continued some time before he was put to death; for from hence he sent two disciples to Jesus, to know if he was the Messiah, Mat 11:2. Now when Jesus heard of this his imprisonment, he departed into Galilee; not so much on account of safety, or for fear of Herod, but to call his disciples, who lived in that country. (s) Antiq. l. 18. c. 7.