Yoga, an Indian art, has been around since at least 15th century, possibly as early as the 10th. It's an ancient practice meant to inspire a connection between mind, body and nature.

Modern yoga, as we know it today, gained popularity about 150 years, slowly trickling down from Indian spiritual leaders to a small population of curious yogis to finally, the masses, David Gordon White, a scholar of yoga and religious studies, writes in Yoga, Brief History of an Idea (PDF ).

The resurgence began in the late 18th century, as Indian writers began to publicize types of meditative yoga as "a unifying sign of the Indian nation," White explains. Hatha yoga, or the flow-and-pose style familiar to most Americans, experienced a resurgence a few decades after meditative yoga gained steam. (All told, there are hundreds of styles of yoga.)

The first few decades of the 20th century saw yoga spreading to people of all ages, locations and nationalities, as seen in the photographs above. As the incredible images demonstrate, yoga began to be prized for its mental and physical benefits.

(MORE: 29 Mind-Boggling Outdoor Yoga Poses )

Today, thanks to an interest in its health impacts, the practice is an international, multi billion-dollar industry, White writes. "In the course of the past 30 years, yoga has been transformed more than at any time since the advent of hatha yoga in the 10th to 11th centuries."

Still, modern yoga retains some of its spiritual roots, as it's commonly practiced at sunrise and sundown to encourage a connection with nature. "Yoga practitioners advise the times around sunrise and sunset, well before eating a meal, as the best time for yoga and meditation practice. The science of biometeorology (the study of natural forces on human and animal life) tells us that the sun has a tremendous impact upon the lives of plants, animals and human beings," Vimala Schneider writes in A Woman’s Guide to Tantra Yoga .

For a look at modern yoga's beginnings, check out the slideshow above.

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