The Bowman is stronger in combat than the Archer, both offensively and defensively, allowing placement in the front line. The Bowman's improved combat prowess helps ameliorate any concern that it may be quickly overrun. The bowman combined with the Walls of Babylon and the Oligarchy (from tradition) in a city is a powerful defense.
We have a fairly accurate picture of the extraordinary Babylonian archer units, thanks to a beautiful Assyrian mosaic showing them marching off to battle. The Babylon archers are dressed in colorful padded robes and carry four-foot long bows, as well as a quiver of arrows slung on their backs. The archers also carry spears or daggers, doubtless for personal defense if enemy units get close enough for hand-to-hand combat.
Separate units carrying large, man-height shields would accompany the bowman, providing in effect, a movable fortress. The bowmen were an integral part of the Babylonian infantry, as their numbers were easier to train and replace than the more expensive cavalry. Bowmen also helped man the famed Walls of Babylon, taking up positions in the many turrets dotting its line.