God of War in Roman Mythology?

The god of war in Roman mythology was Mars. He was worshiped by the soldiers of the legions, temples and altars were erected in his honor, sacrifices were brought to him.
Before the campaign, the legions held whole ceremonies designed to help in the upcoming campaigns and battles.
In Rome, there was the Champ de Mars, on which the army gathered, since the entrance to the city of the army was prohibited (with the exception of triumphs).
Over time, Mars was replaced by other gods who were worshiped by warriors. This lasted until the adoption of Christianity.