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).