Detailed color-lithograph map showing the extensive Union barricades erected in 1861 and '62 to protect Cincinnati from a possible Confederate incursion.
The Ohio River was an extremely vital transit route for the Union, as it linked the Mississippi with the East, and Cincinnati was the most important, potentially-endangered city on the river.
In addition to being an important transit hub for the Union, Cincinnati was also the headquarters of the military Department of the Ohio, which oversaw the region, including the offensives in Kentucky and Tennessee.
In 1862, Cincinnati was under threat of invasion from Confederate Brig. Gen. Henry Heth. The city was placed under martial law and the citizens organized to help expand the earthwork forts and batteries around the city, as described in the present map. Remnants of those fortifications remain today.