PLoS ONE has attempted to discover who these workers were by examining the DNA preserved in their bones. In 2003, hundreds of skeletal remains were unearthed near the mausoleum. They were believed to be the remains of the workers who built the monument, and a preliminary examination of their bones revealed that these men were engaged in heavy manual labor up to their death. But due to poor preservation of the remains, scientists could not determine the ethnic origins of these workers. Since the Qin Dynasty controlled a vast territory and encompassed 22 million people, these workers could have come from anywhere. So Chinese scientists decided to examine the mitochondrial DNA of these workers directly to discover their ethnic origins. These scientists started by collecting DNA samples from 50 thigh bones for analysis. Because ancient DNA analysis is prone to contamination, the researchers took extreme precautions in performing their analysis. In the end, the state of decay of the samples meant the DNA of only 19 individuals could be analyzed. What the researchers found was that these workers had come from a variety of places across East Asia. In fact, the 19 individuals fell into 16 unique maternal haplogroups. The most common haplogroup was N9a, which is thinly spread throughout central and eastern Asia today. Other maternal haplogroups represented included M8a, A, and D5, which are all present among East Asian populations today. Only four of the 19 specimens could be considered ethnically Han, which is the most common ethnic group in China today. Interestingly, seven individuals came from southern China, and a smaller number came from northern China. One individual even carried the maternal haplogroup usually seen only among certain Japanese populations, M7a. The authors conclude that the overall diversity of mitochondrial genetic types seen in these 19 individuals indicates that workers were taken from across China, something that is also asserted in historical records from the period. While further analysis on a greater number of remains is necessary, this initial study has shown that workers from all parts of the burgeoning Qin Empire may have taken part in building some of the first structures of Imperial China.