Thoroughfare Gap is a water gap

Water gap

A water gap is an opening or notch which flowing water has carved through a mountain range. Water gaps often offer a practical route for road and rail transport to cross mountain ridges.- Geology :...

 in the Bull Run Mountains

Bull Run Mountains

The Bull Run Mountains are a mountain range of the Blue Ridge Mountains in northern Virginia in the United States. Located approximately east of the main chain, across the Loudoun Valley...

 created by Broad Run between High Point Mountain

Bull Run Mountains

The Bull Run Mountains are a mountain range of the Blue Ridge Mountains in northern Virginia in the United States. Located approximately east of the main chain, across the Loudoun Valley...

 to the north and Bisquit Mountain

Bull Run Mountains

The Bull Run Mountains are a mountain range of the Blue Ridge Mountains in northern Virginia in the United States. Located approximately east of the main chain, across the Loudoun Valley...

 to the south. It is located on the border of Prince William

Prince William County, Virginia

-National protected areas:* Featherstone National Wildlife Refuge* Manassas National Battlefield Park* Occoquan Bay National Wildlife Refuge* Prince William Forest Park-Government and politics:...

 and Fauquier

Fauquier County, Virginia

As of the census of 2000, there were 55,139 people, 19,842 households, and 15,139 families residing in the county. The population density was 85 people per square mile . There were 21,046 housing units at an average density of 32 per square mile...

 counties in Virginia

Virginia

The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...

.

True to its name, the small gap is traversed by Interstate 66

Interstate 66

Interstate 66 is an Interstate Highway in the eastern United States. As indicated by its even route number, it runs in an east–west direction. Its western terminus is at Middletown, Virginia, at an intersection with Interstate 81; its eastern terminus is in Washington, D.C., at an...

, Virginia State Route 55

Virginia State Route 55

Virginia State Route 55 is a primary state highway in the U.S. state of Virginia. Known for most of its length as John Marshall Highway, the state highway runs from the West Virginia state line, where the highway continues as West Virginia Route 55 , east to U.S. Route 29 in Gainesville...

 and the Manassas Gap Railroad

Manassas Gap Railroad

The Manassas Gap Railroad was an historic intrastate railroad in the Southern United States which ran from Mount Jackson, Virginia to the Orange and Alexandria Railroad at a junction called "Manassas Junction", which later became the city of Manassas, Virginia...

.

The ruins of historic Beverley Mill are located at the gap.

The gap was the site of the 1862 Battle of Thoroughfare Gap

Battle of Thoroughfare Gap

The Battle of Thoroughfare Gap, also known as Chapman's Mill, took place on August 28, 1862, in Fauquier County and Prince William County, Virginia, as part of the Northern Virginia Campaign of the American Civil War. Confederate forces under Maj. Gen. James Longstreet successfully drove back Union...

 during the American Civil War

American Civil War

The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...

.