After General Jackson has handed over the stripe from his cap to Jane Corbin, he is from there on shown in his cap without the stripe. But in the scene where the deserters are executed he's wearing the cape with his stripe back on again.
When Stonewall Jackson is leaving the Virginia Military Institute, as the camera pans past the flagpoles, "New Barracks" can be see. New Barracks wasn't built until 1949. In 1861, all that would have been visible is the iconic "Old Barracks" which was built in 1848.
The style of the stone wall at the sunken road in Fredericksburg is that of the 1930s reconstruction, not that of the original wall. (The stones are larger in cross-section in the reconstruction rather than the original flatter stones.)
While 20th Maine is lined up in loose formation in camp, soldier in front line is smoking or holding in his mouth a bent pipe. The pipe is a Peterson System, made in Dublin, the patent for which wasn't issued until 1894.
As the 20th Maine is storming Marye's Heights, the flag bearer is seen being shot down, with the flag pole breaking in half. He has a green fig leaf tucked under his hat, right above his ear. This indicates that this is a shot taken from footage of the Irish Brigade's attack, since only the Irish soldiers wore these figs (and can be seen putting them on in a deleted scene on the soundtrack's extra features.)
When Colonel Patton speaks his only line in the movie, no one is sitting in front of him or the two men to his right. However, in the previous and subsequent scenes, Generals Longstreet, Lee and Jackson are shown seated in front of Patton and the others.
During the battle of Fredericksburg, it shows brigades charging one after another with a period in between each. However after each brigade is shown charging, the previous brigade seems to disappear from the field. Only a few soldiers are shown falling back, far too few to make up even the most devastated brigades.
During the Battle of Fredricksburg, at the storming of Marye's Heights, a confederate defender is seen being shot in the head (with blood shooting from under his hat.) Later on, he is seen being shot in the head again, this time, from a slightly different angle.
After Jackson is ambushed at night by his own men, the Union begins opening artillery fire on his aids as they rush him back to the road. During one such shot, artillery fires from left to right but in the subsequent shot, with the camera facing in the same direction, the shells from that same firing sequence are seen landing from right to left.
During several shots of the Fredericksburg town battle, St. Peter's Roman Catholic Church is clearly visible. This church is one of the larger landmarks of Harper's Ferry, WV, where many of the Fredericksburg scenes were filmed.
When Joshua Lawrence Chamberlain looks through his binoculars before the Battle of Fredericksburg, he would have been standing on the north side of the Rappahannock River looking at the city towards the south. But the Point of View shot through the binoculars shows what would have been seen looking north from Maryes Heights.
Confederate soldiers at Fredericksburg are shown using cotton bales as parts of fortifications, but cotton was not a Virginia crop, nor was Fredericksburg a shipping point for moving raw cotton to mills in the north.
Robert Edward Lee and Thomas Jonathan Jackson are shown wearing full beards at the very start of the Civil War, but they did not look like this until sometime later. Lee had dark hair going gray and wore a drooping mustache of the type favored by army officers in the 1850s. He grew his well known beard while serving as Jefferson Davis's military advisor. Jackson was clean shaven and grew a beard later out of his well known disinterest in personal grooming and appearance.
The 20th Maine did not charge independently at Fredericksburg. It was part of the 3rd Brigade, 1st Division of the 5th Corp of the Union Army. No lone regiment charge at the Confederate position without supporting regiments around it.
When Jeb Stuart visits Jackson in his camp he introduces himself as a Lieutenant Colonel but he wears the shoulder boards of a full colonel which is a full rank higher (a lieutenant colonel wears a silver leaf while a full colonel displays an eagle). Later in the scene Jackson refers to him as "General Stuart".
After the battle of Chancellorsville it began to rain; General Jackson wore a raincoat on the evening ride, this is shown in the film. After the General is struck and falls from his horse, dirt and dust fly from the ground. After Jackson was put onto the stretcher he was indeed dropped, but this was because the soldiers carrying him slipped in the mud, not because of gunfire.
Before the Battle of Fredricksburg the the Irish Brigades famous green flags were in the process of being replaced, the only regiment to have the green flag was the 28th Massachusetts. Days after the battle Gen. T.F. Meagher, commander of the Irish Brigade, had the new emerald flags presented at what is known as the "Deaths Dinner" while the deaths of their comrades were still fresh on their minds.
During the battle of Fredericksburg, Saint-Clair Augustine Mulholland was a major, not a Lieutenant Colonel. He commanded the 116th Pennsylvania, which was in Meagher's brigade, but not the brigade in total. Meagher made the charge on horseback, and did not 'protect the rear'.
Saint-Claire Mulholland's Regiment the 116th Pennsylvania is depicted leading the Irish Brigade's charge on Marye's Heights, when it was the 28th Massachusetts. The 116th was the only regiment in the Irish Brigade to not have the famous Green Flag but had the state of Pennsylvania flag.
The line from an obviously abridged version of Julius Caesar should be "Liberty, Freedom, tyranny is dead!" "Charity" was the spoken final word in the play in the film, which may have been intentional. It also gives the credits for the actors in the play "Julius Caesar," and spells Caesar incorrectly as "Ceasar."
The goof items below may give away important plot points.
Just before three Confederate deserters are shot we see the deserter nearest the camera get blindfolded with a narrow strip of cloth that barely covers his eyes. On the next shot of them his blindfold is a neatly folded piece of cloth a couple of inches wide.
The musket ball that is said to have come from Jackson's hand is round. Musket balls flatten and expand when entering a body, so if the ball were really extracted from Jackson's hand, it would have been flat, not spherical.