Answer: Italy

The earliest known depiction of the Yin and Yang symbol, the widely recognized symbol of the Taoist philosophical system, was not actually in China, but rather in Italy.

Prior to the formation of Taoism, the use of the Yin and Yang symbol preceded the earliest Taoist versions by a solid 700 years, where the symbol was painted on the shields of Roman soldiers. Specifically, thanks to a well preserved copy of a Roman diplomatic document known as the Notitia Dignitatum, we have illustrations of the shield patterns used by different Roman infantry units. The unit designated as the armigeri defensores seniores bore shields with a symbol remarkably like the modern Yin and Yang.

Despite the clear iconography found on the Roman shields (and later similar iconography found in other cultures), there is no clear relationship between the Roman use of the symbol and the Chinese use of the symbol. Given that many cultures have some philosophical construct to describe the interplay between opposites (such as light and dark, winter and summer, etc.), it’s not unreasonable to think that the artistic representation of these concepts developed independently.