"We estimate that there are at least 75 dead, who were buried very close together in several layers," archaeologist Susanne Friederich said on Friday.
The Battle of Lützen, which took place in 1632, pitted Swedish soldiers against those under the command of German Roman Catholic general Albrecht von Wallenstein.
It was one of the bloodiest battles of the Thirty Years' War, with an estimated 6,500 to 10,000 casualties. The Swedish King Gustavus Adolphus was also mortally wounded during the battle.
The grave was discovered in the late summer of 2011. The 42-square-metre tomb is 1.1 metres deep.
"With the help of anthropological methods, the victims' ages, wounds, causes of death and illnesses will be determined," Friederich added.
The archaeologist said it would take six experts a year to completely unearth the tomb. She said it is thought the dead were buried without clothing, weapons or other personal effects.
Using isotope analysis, the researchers hope to be able to determine the victims' geographic origins. Historical evidence indicates that Germans, Swedes, Finns and Scots fought in the Battle of Lützen.