The purpose of the pommel is to balance the weapon.
The Roman gladii extant have lengths between 14.3 and 23.2 inches. The example shown above represents the Pompeii type which replaced the older Mainz type in the middle of the first century A.D. By contrast, Celtic swords were typically 21 to 33 inches long.
Legionnaires carried the gladius in a scabbard on their right side and they carried a dagger (pugio) in their left side. Some have argued that drawing the sword with the right hand would be too cumbersome while holding the shield in the left hand, but tests have proven that a right side gladius is quite accessible with the right hand. Centurions wore the gladius on the left because they did not carry a dagger.
The spatha eventually replaced the gladius around the year 200 A.D.