Keep up!  You might want to stop walking and start jogging, the Roman Army was expecting its soldiers to march 25 miles a day.  An example of this would be the Magna Iterna.  This marching mode set a pace that forced entire legions to travel 25 miles a day.  While marching, each soldier had to carry his own sarcina, a soldier's pack carried over the shoulder, along with other baggage.  Fast moving groups like scouts would be considered Expeditus, because they are light armed soldiers that can move quickly.

When marching, the line would be set up in a box fashion.  The strongest legions would march in the center.  The strongest of the strongest soldiers marched at the head of the center line.  The legions were called Agmen.   The strongest legion was the Vanguard, going by the name Primum agmen.  Surrounding the strongest legions would be the Novissimum Agmen.  These were the weakest soldiers, they acted as padding in case of a surprise attack.