John Gill Commentary Mark 6:17

"For Herod himself had sent forth and laid hold upon John, and bound him in prison for the sake of Herodias, his brother Philip`s wife; for he had married her." — Mark 6:17 (ASV)

For Herod himself had sent forth Some of his guard, a detachment of soldiers,

and laid hold upon John ; who seized upon him, and took him up:

and bound him in prison ; in the castle of Machaerus:

for Herodias' sake, his brother Philip's wife, for he had married her ; whilst his brother was living, and who had had children by her; (See Gill on Matthew 14:3).