When they were approaching Jerusalem, at Bethphage and Bethany, near the Mount of Olives, he sent two of his disciples and said to them, ‘Go into the village ahead of you, and immediately as you enter it, you will find tied there a colt that has never been ridden; untie it and bring it. If anyone says to you, “Why are you doing this?” just say this, “The Lord needs it and will send it back here immediately.” ’ They went away and found a colt tied near a door, outside in the street. As they were untying it, some of the bystanders said to them, ‘What are you doing, untying the colt?’ They told them what Jesus had said; and they allowed them to take it. Then they brought the colt to Jesus and threw their cloaks on it; and he sat on it. (Mark 11: 1-7)

Mark is pointing the reader to a backstory. But most of us would miss the reference. I would have missed it, except Matthew makes the backstory explicit.

In all three of the synoptic gospels Jesus enact the restoration of Jerusalem as set out by the prophet Zechariah.

Rejoice greatly, O daughter Zion!
Shout aloud, O daughter Jerusalem!
Lo, your king comes to you;
triumphant and victorious is he,
humble and riding on a donkey, on a colt,
the foal of a donkey.

He will cut off the chariot from Ephraim
and the warhorse from Jerusalem;
and the battle-bow shall be cut off,
and he shall command peace to the nations;
his dominion shall be from sea to sea,
and from the River to the ends of the earth.

Zechariah 9:9-10

Zechariah is one of the most visionary and metaphorical in scripture. In the 9th chapter Jerualem is restored. Five chapters later Jerusalem is horribly destroyed and God's reign is extended across the earth.

Above is the White Donkey by June Rydgren.