Eleven of the fifteen costliest battles of the Civil War were fought in the Eastern Theater (in bold):

	battle	date	casualties
1	Gettysburg	July 1-3, 1863	51,000
2	Chickamauga*	Sept. 18-20, 1863	35,000
3	Spotsylvania	May 8-21, 1864	30,000
4	The Wilderness	May 5-7, 1864	29,800
5	Chancellorsville	May 1-3, 1863	24,000
6	Shiloh*	April 6-7, 1862	23,700
7	Stones River*	Dec. 31, 1862-Jan. 2, 1863	23,500
8	Antietam	Sept. 17, 1862	22,700
9	Second Bull Run (Manassas)	Aug. 28-30, 1862	22,200
10	Fredericksburg	Dec. 11-15, 1862	17,900
11	Fort Donelson*	Feb. 11-16, 1862	17,400
12	Cold Harbor	May 31-June 12, 1864	15,500
13	Gaines’ Mill	June 27, 1862	15,500
14	Seven Pines	May 31-June 1, 1862	13,700
15	Harpers Ferry	Sept. 12-15, 1862	12,900

Notes:

Eastern Theater battles are in bold. Western Theater battles are marked with an asterix.

“Casualties” includes killed, wounded and captured or missing from both sides. Almost all the casualties from Harpers Ferry consisted of the captured Union garrison and 70% of the casualties from Fort Donelson were of the captured Confederate garrison.

Antietam, one of two single day battles in the top 15, was the bloodiest single day of the Civil War and in American military history.