The term "triarii" refers to a specific group of soldiers in the ancient Roman army, particularly during the Republic period. They were part of the Roman legion and represented the third line of infantry in the traditional battle formation. Triarii were typically experienced veterans, equipped with heavy armor and long spears, known as hastae. Their role was to serve as a reserve force, stepping in during critical moments of battle when the front lines were faltering. Triarii were crucial for maintaining the stability of the Roman military structure. When the first two lines, known as the hastati and principes, faced overwhelming pressure, the triarii would advance to reinforce them. This strategic deployment allowed the Romans to adapt to changing battlefield conditions and often turned the tide in their favor. The presence of triarii underscored the importance of experience and discipline in the Roman military.