Ashigaru formed the backbone of samurai armies in the later periods. The real change for the ashigaru began in 1543 with the introduction of matchlock firearms by the Portuguese. Almost immediately local "daimyōs" started to equip their ashigaru with the new weapon that required little training to use proficiently, as compared to the longbow which took many years to learn. As battles became more complex and forces larger, ashigaru were rigorously trained so that they would hold their ranks in the face of enemy fire.