Taijitu (a Chinese word that translates roughly as ‘diagram of ultimate power’) is a term which refers to any of the Chinese symbols for the concept of yin yang, and is sometimes extended to similar geometric patterns used historically by various cultures. The most recognized form is composed of two semi-circular teardrop-shaped curves of different colors, or a circle separated by an S-shaped line, where each half is marked with a dot in the opposite (or different) color. Symbols of this type are found as Celtic art forms and coat of arms for several Western Roman army units in Late Antiquity. Taoist philosophy adopted equivalent symbols several hundred years later, as representations of yin and yang, from which the most common modern usage of the symbol and the name ‘taijitu’ arise. There is no academically established relationship between the Taoist and the earlier ancient Roman symbols.
Symbols with a partial resemblance to the later Taoist diagram appeared in Celtic art from the 3rd century BC onwards, showing groups of leaves separated by an S-shaped line. The pattern lacked the element of mutual penetration, though, and the two halfs were not always portraited in different colours. A mosaic in a Roman villa in Sousse, Tunisia, features different colors for the two halves of the circle, but here, too, the little circles of opposite color are absent.
The earliest depiction of the diagram which today is known as Taijitu or Taiji appears in the Roman Notitia Dignitatum, an ancient collection of shield patterns of the Roman army dated to ca. AD 430. The emblem of an infantry unit called the armigeri defensores seniores (“shield-bearers”) is graphically identical in all but colour to the dynamic, clockwise version of the Far Eastern tradition. Another Western Romandetachment, the Pseudocomitatenses Mauri Osismiaci, featured an insignia with the same contours, but with the dot in each part kept in the same shade of colour. A third infantry regiment, the Legion palatinaeThebaei, had a shield pattern comparable to the static version of the East Asian symbol: three concentric circles vertically divided into two halfs of opposite and alternating colors, so that on each side the two colors follow one another in the inverse order of the opposite half. The Roman yin-yang-like symbols predate the Taoist version by several hundred years:
As for the appearance of the iconography of the “yin-yang” in the course of time, it was recorded that in China the first representations of the yin-yang, at least the ones that have reached us, go back to the eleventh century AD, even though these two principles were spoken of in the fourth or fifth century BC. With the Notitia Dignitatum we are instead in the fourth or fifth century AD, therefore from the iconographic point of view, almost seven hundred years earlier than the date of its appearance in China.
It should be mentioned that there is no academically established relationship between the ancient Roman and the later Taoist symbols.
The Taijitu or Taiji diagram is a well known symbol representing the principle of yin and yang, introduced in China by Ming period author Lai Zhide. The term taijitu (literally “diagram of the supreme ultimate”) is commonly used to mean the simple ‘divided circle’ form, but may refer to any of several schematic diagrams representing these principles, such as the one at right.
In the taijitu, the circle itself represents a whole (see wuji), while the black and white areas within it represent interacting parts or manifestations of the whole. The white area represents yang elements, and is generally depicted as rising on the left, while the dark (yin) area is shown descending on the right (though other arrangements exist, most notably the version used on the flag of South Korea). The image is designed to give the appearance of movement. Each area also contains a small circle of the opposite color at its fullest point (near the zenith and nadir of the figure) to indicate how each will transform into the other.