Discover the Longest Tunnel in Mississippi

Written by Angie Menjivar
Updated: August 4, 2023
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Key Points:
  • The longest tunnel in Mississippi is Thayer’s Approach Tunnel, constructed by the Union Army during the Civil War during the Battle of Vicksburg.
  • Originally intended as a trench, the soldiers realized that if the trench was covered by bundles of cane the makeshift roof protected them from being hit by ammunition. So, they decided to keep digging until they were close enough to stage a surprise attack.
  • Vicksburg surrendered before the tunnel was complete, but it remains at the Vicksburg National Military Park in Vicksburg, Mississippi.

In Mississippi, tunnels aren’t common. Despite this, however, there is one tunnel worth mentioning. Many other tunnels found throughout the U.S. are significantly longer, often for passenger vehicles, and sometimes even for traveling underwater. However, this unique, longest tunnel in Mississippi serves as a rousing historical attraction.

Surprisingly, it’s little known but it played a pivotal role in the Civil War during the battle of Vicksburg. Today, it’s part of a national military park where other monuments and markers are on display, and where several wildlife animals thrive.

Even though it’s the site of one of the bloodiest battles, the park epitomizes resilience.

Infographic of Thayer’s Approach Tunnel
Vicksburg National Military Park includes historical markers, monuments, and the Thayer’s Approach Tunnel.

When Was Thayer’s Approach Tunnel Built?

Cannons at Vicksburg National Military Park

Vicksburg National Military Park in Vicksburg is where the longest tunnel in Mississippi can be found.


Thayer’s Approach Tunnel is the longest tunnel in Mississippi. It is located in Vicksburg, Mississippi. It was initially built by Union soldiers during the Civil War when they were under the command of Brigadier General John M. Thayer.

At the time, they were working to attack the Confederacy but found themselves at a disadvantage. The Confederates had set themselves up on a ridge about 200 feet above the Union soldiers. Any approach would have made them vulnerable to sharpshooters. They made two failed attempts at first and then decided they’d use the earth itself as cover.

The soldiers started digging using only picks and shovels. Their aim was to create a 6-foot-deep trench to prepare for their next assault attempt. Aside from digging into the earth, they also placed bundles of cane (known as fascines) on top of the tunnel they were excavating to create a makeshift roof.

Not only did the roof serve as cover, but it was also strong enough to prevent bullets from making contact with the soldiers huddled under it. Their plan was to keep digging to get close enough to the Confederates so they could surprise attack with a mine.

However, they didn’t need to execute the final plan. Before the Union soldiers could see it to fruition, Vicksburg surrendered. Today, the tunnel is a part of the Vicksburg National Military Park, which was established in 1899.

The site serves to commemorate the soldiers who took part in the battle. It’s filled with a variety of historical markers, including homes, monuments, and, of course, the Thayer’s Approach Tunnel. This tunnel played an important role for the Union and holds a piece of history within its walls.

Thayer's Approach, Vicksburg National Military Park

Thayer’s Approach Tunnel is the longest tunnel in Mississippi.

©Ken Lund / Flickr – License

What Is Thayer’s Approach Tunnel’s Primary Purpose?

When Thayer’s Approach was constructed, it served a vital purpose to conceal and protect Union soldiers facing attack by the Confederates. They initially had the plan to keep digging until they got close enough to the Confederates to execute their own attack.

However, they did not need to follow through with this plan. Today, Thayer’s Approach serves no other purpose than to remind the nation of the events that transpired that day. It also serves to commemorate the soldiers who took part in the siege and defense of Vicksburg.

Thayer’s Approach Tunnel is part of a 1,800-acre park, surrounded not just by markers and monuments, but also by miles of trenches. When you stand at one opening of Thayer’s Approach, you can clearly see through the other side.

Though the most unique and longest tunnel in Mississippi, it’s not comparable to some of the other tunnels found throughout the United States. It wasn’t meant as a passageway for vehicles or trains. Rather, it was meant for a group of soldiers looking for a way to protect themselves while they executed a plan of attack.

Cannons at Vicksburg National Military Park

These cannons are now a Civil War monument at the Vicksburg National Military Park in Vicksburg.


Wildlife Surrounding Thayer’s Approach Tunnel

Vicksburg National Military Park is designated as an Important Bird Area (IBA). This is because it is located under the Mississippi migratory flyway where more than 325 bird species make their way from Canada and the northern part of the U.S. down to their wintering grounds as far south as South America, but also to Central America and along the Gulf of Mexico.

Some of the protected birds include prothonotary warblers, least terns, and whooping cranes. You can also spot eastern kingbirds, Mississippi kite, summer tanagers, eastern bluebirds, and even rare bald eagles.

Reptiles and plant species also rely on Vicksburg National Military Park as a haven. Several of the eldest second-growth trees call the park home. While walking through the park, you may just have a chance encounter with a bobcat. You can identify them by their distinctive appearance. They have beige fur and short tails and may have either line or spotted markings.

In the areas surrounding the park, there are several other animal species, including armadillos (which have made their way to the south of the U.S. from Central America) and American alligators (that grow up to 15 feet long and may weigh up to 500 pounds), which are best enjoyed from a safe distance!

Where Is Thayer’s Approach Tunnel Located on a Map?

Thayer’s Approach Tunnel is located within the Vicksburg National Military Park. The landmark Old Court House has a museum displaying Civil War artifacts, while the Lower Mississippi River Museum features an aquarium and interactive exhibits.

Vicksburg is a city in western Mississippi and it is known as the site of a key Civil War battle. The Siege of Vicksburg is commemorated at the vast Vicksburg National Military Park, which encompasses the Vicksburg National Cemetery and the restored USS Cairo gunboat.

Here is Vicksburg, Mississippi on a map:

The photo featured at the top of this post is © Sean Pavone/

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About the Author

Angie Menjivar is a writer at A-Z-Animals primarily covering pets, wildlife, and the human spirit. She has 14 years of experience, holds a Bachelor's degree in psychology, and continues her studies into human behavior, working as a copywriter in the mental health space. She resides in North Carolina, where she's fallen in love with thunderstorms and uses them as an excuse to get extra cuddles from her three cats.

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