Expositor's Bible Commentary Commentary Mark 15:18

"and they began to salute him, Hail, King of the Jews!" — Mark 15:18 (ASV)

The soldiers thought it was a great joke that this gentle Jew claimed to be a king. So they took a purple robe, a symbol of royalty, and threw it across his shredded and bleeding back. The crown was made of some kind of prickly plant such as abounds in Palestine. This they pressed into his scalp. Again there must have been copious bleeding because the scalp is one of the most vascular areas of the body. They mocked him with a parody of “Hail, Emperor Caesar!”