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Let's say you're in charge of a group of laborers anywhere from the Iron Age to the Middle Ages.
Your job is to build a dike made of earth, a couple of meters high and presumably about the same width (since the angle of repose of shoveled earth isn't very steep). You have shovels and any other tools of the era.
How many man-days of labor does it take per meter of dike?
Primary sources would be best, but modern reconstructions using historical techniques would be acceptable.
Julius Caesar is alleged to have completed a 25 mile double circumvallation (11 miles inner, 14 miles outer) of Alesia in 30 days, with approximately 50,000 men - though at all times, of course, some of those had to be on guard duty. This circumvallation would have been a 8 foot or so ditch in front of a similar mound, on which a 12-15 foot wooden wall was built, with fortified camps acting as keeps and with towers at regular intervals.
If we assume half the men on guard duty at a time, with 12 hour days, that is
5,280 * 25 = 132,000 feet of fortifications
built in
25,000 * 30 * 12 = 9,000,000 man-hours
or approximately
9,000,000 / 132,000 = 68
labour-hours per foot of fortifications.
Other than the fortified camps, which would have been assembled initially with materials from the Legionnaires regular pack, all materials would have been manufactured for single use at this one location. Most of the artillery (catapults, mangonels, and such) would likely have come from the Caesar's baggage train. Also the head count is strictly fighting men, and camp followers capable of assisting in the construction might have been an equal number - though none of them would have had to provide guard duty. This provide an upper limit to accompany the lower limit above, of perhaps 200 labour-hours per foot of fortification, giving a estimated range of 65-200 labour hours per foot of fortification.
The process of moving earth with a shovel or other manual tools hasn't change much on the centuries. In fact, the amount of man-hours needed to manually excavate or lay a cubic meter of earth depends on a lot of factors, including the kind of earth (loose-hard), the form of excavation, how far is the trench and the dike (assuming you are taking earth from the trench to lay it in the dike) and so, and I think the century would be a minor factor. In fact, what is succinctly described in Wikipedia:Roman_military_personal_equipment#Entrenching_tools doesn't seem very different of the tools that we would use nowadays to do manually the same task.
In the building industry there are data banks with estimates of manpower and material needed to perform a lot of tasks - those used to be books, now they are computer databases. Those banks still include some manual earth moving tasks.
To give an order of magnitude, I've checked a couple of manual tasks in a data bank I have at hand:
Loading a truck is probably among the easiest earth-moving tasks, but excavating a trench might be more similar to building fortifications. However, the harder the earth, the slower the task. Additionally, building a dike needs some compacting that is not included on those estimates.
Therefore, a reasonable ballpark estimate is a few man-hours per cubic meter of fortification, the particular amount depending on a lot of circumstances of the site.
Additionally, we should have in mind that building a fortification is more than just earth-moving. Those additional tasks are not included in this estimate.
