Complex sentence: On July 3 at 1:00 pm the artillery barrage from 140 Confederate cannons started, and at 3:00 pm, the Confederates formed a battle line to march across a mile of open field.
Split into simpler sentences: On July 3 at 1:00 pm the artillery barrage from 140 Confederate cannons started. At 3:00 pm, the Confederates formed a battle line to march across a mile of open field.