Or were just good enough to dig the ditches.
“Interesting that a goodly number of “Barbarians” had the skills necessary to provide for the First Emperor.”
The article includes this passage, indicating they were not voluntary or skilled laborers: “Some bones were thickset with different extent of arthritis, and others bore fractures or obvious adaptation structures caused by intense pull from muscle, suggesting that these people were engaged in heavy work before death. Furthermore, given their casual and layer-on-layer burial accompanied by potsherds, iron tools, and several instruments of torture in a 10-meter deep tomb, they would have been of very low social status.”