An archer shoots an arrow in the air horizontally

An archer shoots an arrow in the air horizontally. However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain why the arrow ultimately falls down.
The archer stretches the string of the bow by applying muscular force. In the process the shape of the bow changes. When the string is released, it regains its original
position that provides the initial force to set the arrow in motion. The force of gravity that acts on the arrow in the downward direction brings it to the ground.