Battlefield role
Holds the line, absorbs damage for fragile units behind it, and clears lightly defended positions.
The swordsman is the backbone unit of the early ages: not the fastest, not the hardest-hitting, but the one you can build a plan around. Most armies in the first half of the game are measured by what happens when their swordsman line meets yours.
Their real job is protection. Archers, siege engines, and workers all live longer when a swordsman wall stands between them and the enemy. An unsupported swordsman blob, though, is target practice for ranged forces — bring answers, or bring shields.