From Rhetorica ad Herennium written at around 80 bc:

"We ought, then, to set up images of a kind that can adhere longest in the memory. And we shall do so if we establish likenesses as striking as possible; if we set up images that are not many or vague, but doing something; if we assign to them exceptional beauty or singular ugliness; if we dress some of them with crowns or purple cloaks, for example, so that the likeness may be more distinct to us; or if we somehow disfigure them, as by introducing one stained with blood or soiled with mud or smeared with red paint, so that its form is more striking, or by assigning certain comic effects to our images, for that, too, will ensure our remembering them more readily."
Does that ring a bell? Let's compare with the gospel of Mark at 15:16 it says:

"The soldiers led Jesus into the courtyard of the palace (that is, the governor’s headquarters) and called out the whole guard. They dressed him in a purple robe, twisted some thorns into a victor’s crown, and placed it on his head. They began to greet him, “Long live the king of the Jews!” They kept hitting him on the head with a stick, spitting on him, kneeling in front of him, and worshiping him. When they had finished making fun of him, they stripped him of the purple robe, put his own clothes back on him, and led him away to crucify him."
Also from John 19:33-34
"But when they came to Jesus and saw that he was already dead, they did not break his legs. Instead, one of the soldiers pierced his side with a spear, and blood and water immediately came out."

Could it be that these parts have been added later for the purpose of making the image of the crucifixion of Jesus more striking? Any thoughts?