120 steps per minute, each 30 inches long = 4 miles per hour.

That's the US Army's marching beat on level ground (e.g., a street or parade ground), without pack but with weapon, canteen, etc.. This is usually done for 50 minutes followed by a 10 minute break.

In the past I've kept that pace for as much as 10 hours (with breaks for food). Our total distance covered was about 32 miles, as I remember.

Walk 10 minutes, jog or run 5, is also an interesting (and ground covering) exercise).