Bernini’s patron Cardinal Scipione Borghese  comissioned the David sculpture for his personal villa. The twenty-four year old Bernini completed the work in seven months. The sculpture depicts the scene as described in Samuel 17 of the Old Testament: 

When the Philistine Goliath arose and came and drew near to meet David, David ran quickly toward the battle line to meet the Philistine. And David put his hand in his bag and took out a stone and slung it and struck the Philistine on his forehead. The stone sank into his forehead, and he fell on his face to the ground.

Bernini shows us David at the critical moment in his fight with the Philistine champion Goliath. David has placed his harp on the ground between his legs. His torso is twisted like a coil ready to spring. His face, and especially his lips, concentrate the intensity of the moment into a single expression of determination.

The Three Davids: before, during, and after the combat

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(Image source: https://richardnilsen.com/tag/bernini/0