Final answer:
Giotto's fresco 'Christ Entering Jerusalem' depicts Palm Sunday, the event of Jesus Christ's entry into Jerusalem as described in the Gospels, marked by the crowds' welcoming gestures.
Step-by-step explanation:
The event depicted in the fresco 'Christ Entering Jerusalem' by Giotto is Palm Sunday. This scene is part of the Christian narratives that describe Jesus Christ's triumphant entry into Jerusalem, as recounted in the Gospels of Matthew, Mark, Luke, and John. On this day, Jesus rode into the city on a donkey as a symbol of peace, and he was welcomed by crowds who spread palm branches and cloaks on the ground before him as a sign of honor and recognition of his prophesied arrival.
In the context of Christian art, this event is often captured to reflect the joyful yet poignant beginning of the final week of Jesus' life, leading up to his crucifixion. Giotto's depiction in the Arena Chapel captures this moment with the distinct use of realism and emotional depth that characterized his departure from the medieval traditions of spiritual representation.