Some of the 55,000 runners of the Peachtree Road Race struggling up Cardiac Hill.

Christy Cullen/flickr

On July 4, 1969, a group of running enthusiasts had just wrapped up a less-than-inspiring race at Ft. Benning in Columbus, Ga. and was making the hour-and-a-half drive back to Atlanta when someone in the car threw out an idea. Why drive far away to some small town for a modest road race when they could just run their own road race in Atlanta during the Independence holiday?

The group was part of the Atlanta Track Club, still in its relative infancy, and the race these runners came up with on that car ride home would become one of the most popular 10Ks ever. Little did they know what they'd spawned.

Held annually every Fourth of July, the Atlanta Journal-Constitution Peachtree Road Race is the most popular 10K race in the United States. Staged for the first time in 1970 by the Atlanta Track Club, the race now holds the title of largest 10K in the world. In 2008, the Vancouver Sun Run had more than 59,000 entrants turn out for its 2.5K and 10K combo run, and more recently the Bolder Boulder 10K in Colorado has grown to nearly equal the size of the Peachtree (54,040 entrants in 2008) [source: Daily Camera]. However, at 55,000 entrants, the Peachtree Road Race still has the title of the largest 10K. But it didn't start out that way.

That first race in 1970, 110 runners showed up at the old Sears parking lot at the corner of Peachtree and Roswell roads. The popularity of the race grew almost exponentially over its first 10 years. It nearly doubled in size every year during that first decade until organizers capped registration at 25,000 entrants in 1980. It stayed that way until 1990 when it grew to 40,000 before capping at 55,000 in 1998 [source: Atlanta Track Club]. So what makes the Peachtree Road Race so popular?

That's what you came here to find out. Let's take a look at why the Peachtree Road Race is considered one of the top road races of any distance. We'll start by learning what you need to do to enter.