I've always been curious when reading about battles in the pre-modern era as to what methods they would employ to properly assess the death toll afterwards.
Specifically, I've been really interested in how people figured out the number of dead after major sieges, such as the Siege of Carthage, in which as many as ~500,000 people were apparently killed. It seems like an incredible undertaking to record with accuracy such results.
Why do you assume the results were accurate?
The Spartans used to have a twig that they would mark at each end and then break it in half, leaving one half at the camp and the other with them. Once the battle finished the survivors reclaimed their half left at the camp and the remainder were counted. However in ancient times casualty figures were more to do with propaganda than fact so accurate figures just don't exist