One prime example is Antietam, or Sharpsburg. In a single day battle, from just before dawn to after dark on a long summer day, a combined 26,134 men were killed. Many of these were in a thick cornfield where confusion ruled the fighting. No one could see the enemy, and many shot their own ranks in front of them.
Point being, it really puts our casualty numbers in Iraq in a different perspective.
Estimates are 22,720 total casualties, of which 3,650 were killed, 17,300 wounded, and 1,770 missing/captured. You can verify my numbers at:
http://www.nps.gov/anti/casualty.htm