Zechariah inverted every royal expectation: 'Rejoice greatly, O daughter of Sion, shout for joy, O daughter of Jerusalem: BEHOLD THY KING will come to thee, the just and saviour: he is poor, and RIDING UPON AN ASS, and upon a colt the foal of an ass' (Zechariah 9:9) — not a war-horse but a beast of burden; the verse continues by abolishing the chariot and the bow and promising peace to the nations.
The fulfillment is one of the few Christ arranged with explicit deliberation: from Bethphage on this hillside He sent two disciples for the colt 'on which no man ever hath sitten,' and rode it down the Mount of Olives into the city while the crowds spread garments and palm branches and cried 'Hosanna to the son of David' (Matthew 21:1–9; Mark 11; Luke 19; John 12). Matthew and John both cite Zechariah's verse over the scene.
John adds the honest note of an eyewitness tradition: 'These things his disciples did not know at the first; but when Jesus was glorified, then they remembered that these things were written of him' (John 12:16). The Church has re-enacted the prophecy every Palm Sunday since at least the fourth century, when the pilgrim Egeria described the Jerusalem procession down this same road.