The Union ambitiously tunneled 511 feet to reach the Confederate lines during siege of Petersburg, Virginia, in 1864. Unique to this Civil War battle, they set off a massive explosion that created a 170-by-120-feet crater beneath the Confederate lines and stormed the defenses in a failed effort, known as the Battle of the Crater. Thereafter, the Confederates worried that Union forces might again strike from under the ground. The South’s tactical response was to construct tunnels called countermines to detect Union digging.
A research group called the Petersburg Project wishes to draw attention to the role Confederate countermines played at Petersburg. They have researched a map from the Library of Congress, in conjunction with conducting battlefield archeology and examining LIDAR images, to determine the precise locations of many Confederate tunnels. The map titled [Map of defenses Petersburg, Virginia, showing the position of General Lee and his staff during the attack on Fort Stedman, March 25, 1865] is one of the earliest known Union surveys of the battlefield. The map is untitled is mixture of ink and pencil, suggesting that it is a proof. The locations of forts, defenses, and railroad tracks are clearly identifiable. The red lines indicate topography. In the background are thinly penciled lines that denote triangulation points for mapping. However, in some cases, the penciled lines represent tunnels.
The Petersburg Project team were able to make the intellectual leap that some of the penciled lines represent tunnels, because they had read accounts of Confederate countermines at Petersburg, which appear in the official government history of the Civil War titled The War of Rebellion. Armed with that knowledge, the researchers concentrated their work on Confederate countermines in a sector of the battlefield known as Gracie’s Salient. It was there the Confederates exploded a portion of their own countermines, on July 31, 1864, to destroy forward-extending Union trenches, known as saps, where sharpshooters operated. Cartographic evidence of the Confederate tunnels in Gracie’s Salient appears on the aforementioned 1865 map in the shape of penciled lines.
The penciled lines contrast with Union engineer Nathaniel Michler’s later map, where the aforementioned lines are represented in ink, notes the Petersburg Project. Nonetheless, they are not labeled as tunnels and therefore easily mistaken for trenches.
A breakthrough happened when the researchers compared the 1865 map with LIDAR images that showed impressions in the land matching the path of the tunnels on the map. With that evidence, the researchers believed they had located the Confederate tunnels at Gracie’s Salient.
Other discoveries of Confederate tunnels at Petersburg have been less related to science and were more so an accident. In one case a mule pulling a plow disappeared into a hole and in another a tunnel was happened upon during construction work in the 1970s. A photograph of one tunnel can be seen here.
As for the battle itself, the Siege of Petersburg began June 15, 1864 and lasted to April 2, 1865. It was fought about 25 miles outside the Confederate capital of Richmond, Virginia, and was a costly grind, resulting in some 70,000 casualties. The siege was a defining chapter in the war and signaled the downfall of the Confederacy. The Union eventually forced Robert E. Lee and the Army of Northern Virginia to take flight to avoid being cut off from supplies. In hot pursuit, the Union forces under Ulysses S. Grant quickly outmaneuvered the worn out Confederates and negotiated their surrender at Appomattox, Virginia, on April 9, 1865. Although these events have long passed, the 1865 map shows that there is still much to rediscover about this momentous period of American history.