Province Size?

[Hakko]

I got this little bit of info from this site:

The first thing the soldiers were taught to do, was to march. The historian Vegetius tells us that it was seen as of greatest importance to the Roman army that its soldiers could march at speed.
Any army which would be split up by stragglers at the back or soldiers trundling along at differing speeds would be vulnerable to attack.
Hence right from the beginning the Roman soldier was trained to march in line and to keep the army a compact fighting unit on the move.
For this, we are told by Vegetius, during the summer months the soldiers were to be marched twenty Roman miles (18.4 miles/29.6 km), which had to be completed in five hours.

I presume this speed was over a Roman road, rather than rough terrain. It also mentions that a legion was expected to begin a campaign with 16 days' rations, which, along with other equipment, weighed in at somewhere between 66 and 93 pounds (30-41 kg). So, theoretically, in sixteen days, a legion cold march ~480 kilometers (300 miles) without resupply. I imagine that actual pace was slower, since sustaining that kind of speed over that long would probably kill the unit as a fighting force.