Vicksburg was fascinating, as we knew it would be.

Grant knew that control of the Mississippi River was crucial, both in allowing Union supplies and forces to move north and south, and conversely to prevent munitions and supplies from reaching the Rebels.  And also to cut off Texas, Arkansas, and Louisiana from the rest of the Confederacy. The Union siege of Vicksburg took nearly two months; the city finally fell on the 4th of July, 1863, and is considered a turning point on the war. 

This is a view of the river, and the field on which the Union finally beat back the Confederate strongholds, after multiple attempts.