“put him in prison.” According to the records we have from Josephus, Herod Antipas put John in prison at Machaerus, his palace-fortress east of the Dead Sea. Machaerus was originally built about 90 BC by the Hasmonean king, Alexander Jannaeus (104 BC-78 BC). It is located about 15 miles (24 km) south and east of the point at which the Jordan River enters the Dead Sea. In 57 BC it was destroyed by Pompey’s general Gabinius, but rebuilt by Herod the Great in 30 BC. Machaerus was the easternmost palace-fortress of Herod, and he strongly fortified it, in part due to its proximity to Arabia.
When Herod the Great died, the palace-fortress Machaerus was passed to his son, Herod Antipas, who ruled from 4 BC until 39 AD, and who imprisoned and beheaded John the Baptist at Machaerus. Because Herod the Great built his palace in the center of the fortified area, we know the location Salome was when she danced before Herod Antipas and his guests and asked for the head of John the Baptist. Machaerus passed from Herod Antipas to Herod Agrippa I, and when he died in 44 AD, it came under Roman control. Jewish rebels took control after 66 AD during the First Jewish Revolt, but the Romans began a siege of the fortress in 72 AD. They built a wall of circumvallation around the fortress, and an embankment and ramp for the Roman siege engines, but the Jewish rebels surrendered before the Romans began their attack. The rebels were allowed to leave and the Romans tore the palace-fortress down, leaving only the foundations, which are still there today.
Some scholars think John was in prison for two years at Machaerus, but that is because they think Jesus had a three-year ministry. There is good evidence that Jesus’ ministry lasted only shortly over a year, from before Passover in 27 AD to Passover in 28 AD, and therefore the imprisonment of John would have been considerably less than a year. It seems that John was put in prison not too long after he baptized Jesus because Jesus had not yet gone into Galilee and started his teaching nor had called out his disciples to follow him, who were later to be the apostles (Mark 1:14-16). However, John was imprisoned after Passover of 27 AD (compare John 2:13ff with John 3:22-24). John the Baptist was beheaded by Herod Antipas at his birthday celebration, but unfortunately, we do not know when Herod’s birthday was. However, it was before the feeding of the 5,000 (Matt. 14:13ff; Mark 6:32ff; Luke 9:10ff; John 6:1ff), and thus before the feast of Tabernacles, which occurred in our September/October (John 7:1ff). Actually, it was likely some months before Tabernacles, likely sometime in the summer months. Thus, if John was imprisoned in our April or May of 27 AD, and beheaded by October that same year at the latest, the most he would have been in prison is 6 months, but it was likely a much shorter time.