On a vast, grassy plot of land 150 miles northwest of Istanbul, the scene will play out the first week in July, much as it has for the past 646 years. Nearly 2,000 men and boys will trek from all over Turkey to the Field of Heroes, near Edirne, to slather themselves with olive oil and face off at Kirkpinar (translation: 40 Springs), the national oil-wrestling tournament. Started by soldiers during the time of the Ottoman Empire and named, according to legend, for mysterious springs that arose at Edirne after two warriors fought there to the death, the three-day, greased-up extravaganza is the oldest ongoing sporting event in the world.

It's also one of the most grueling. Since its inception, in 1362, the rules have been simple: no water breaks, no timeouts. Officials imposed a 40-minute time limit on matches in 1975, but wrestlers in 13 divisions still risk scars and broken teeth in temperatures nearing 100° for the chance to snag medals and money. The winner of the top class also earns the prestigious golden belt as the bas pehlivan—head wrestler. But for many Turks, competing at Kirkpinar means more than the chance to win cash and acclaim.

"This is our ancestral sport," says 22-year-old Mustafa Yenisancak, who's wrestled at Kirkpinar since he was 8. "It's our cultural duty."

Check out the photo gallery below for more.