Researchers in China have positively identified a block of ancient vegetable matter as tiny tea buds that were lovingly tucked away in Han Yangling Mausoleum, a sumptuous tomb north of Xi'an. The city Xi'an was once known as Chang'an, seat of power for the Han Dynasty, and stood as the easternmost stop on the vast trade routes known today as the Silk Road. Previously, the oldest physical evidence of tea came from roughly 1,000 years ago. Coupled with another ancient block of tea found in western Tibet's Gurgyam Cemetery, this new discovery reveals that the Han Chinese were already trading with Tibetans in 200 BCE, trekking across the Tibetan Plateau to deliver the luxurious, tasty drink.

Though the tea was excavated over a decade ago, it wasn't until recently that researchers had access to tests that could determine whether the vegetable matter was in fact tea. By untangling the chemical components of the leaves, including their caffeine content, the researchers were able to verify that both blocks of leaves, from China and Tibet, were tea. In fact, they even figured out what kind of tea it probably was. In Nature Scientific Reports, they write:

The sample contains a mixture of tea, barley (Hordeum vulgare, Poaceae) and other plants. Therefore, it is likely that tea buds and/or leaves were consumed in a form similar to traditionally-prepared butter tea, in which tea is mixed with salt, tsampa (roasted barley flour) and/or ginger in the cold mountain areas of central Asia. Of course, methods of brewing and consuming tea varied from culture to culture along the Silk Road.

We also know the tea was what people today would call "fine plucked" or "Emperor's Tea," because it consisted only of the plant's buds with a few small leaves. These parts of the plant are considered the most valuable and are used to make especially high-grade tea.

But the discovery isn't just about how delicious beverages could be two millennia ago. It's also about trade.

Travelers were criss-crossing the Asian continent for thousands of years before Han Dynasty notables were sipping tea in Chang'an. Those early wanderers brought seeds and agricultural practices to people all over western China and beyond. But those journeys were few and far between. These new discoveries of tea, however, offer a possible start date for regular trade routes between China and its neighbors. As early as 2,100 years ago, a proto-Silk Road was in operation. Traders of that era probably took a previously unknown route between Chang'an and Tibet, far south from the routes that became common in the Tang Dynasty or Middle Ages.

Though it would be hundreds of years before the great cities of the Silk Road rose to prominence, these 2,100-year-old tea leaves let us glimpse the possible origins of the world's most awe-inspiring trade routes.

Nature Scientific Reports, DOI: 10.1038/srep18955