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. (May 2014)
In antiquity, field signs or standards were used in warfare that can be categorised as vexilloid or 'flag-like'. This is considered originated in the ancient Egypt or Assyria. Examples include the Sassanid battle standard Derafsh Kaviani, and the standards of the Roman legions such as the eagle of Augustus Caesar's Xth legion, or the dragon standard of the Sarmatians; the latter was let fly freely in the wind, carried by a horseman, but judging from depictions it was more similar to an elongated dragon kite than to a simple flag.
Flag as recognized today, made of a piece of cloth representing a particular entity, is considered invented in the Indian subcontinent or Chinese Zhou dynasty (1046-256 BCE). Chinese flags depicted animals decorated in certain colors. A royal flag is considered being used as well, which was required to be treated with a similar level of respect attributed to the ruler. Indian flags were often triangular shaped and decorated with attachments such as yak's tail and the state umbrella. These usages spread to Southeast Asia as well, and considered transmitted to Europe through the Muslim world where plainly colored flags were being used due to Islamic prescriptions.
In Europe, during the High Middle Ages, flags came to be used primarily as a heraldic device in battle, allowing more easily to identify a knight than only from the heraldic device painted on the shield. Already during the high medieval period, and increasingly during the Late Middle Ages, city states and communes such as those of the Old Swiss Confederacy also began to use flags as field signs. Regimental flags for individual units became commonplace during the Early Modern period.
During the peak of the age of sail, beginning in the early 17th century, it was customary (and later a legal requirement) for ships to carry flags designating their nationality; these flags eventually evolved into the national flags and maritime flags of today. Flags also became the preferred means of communications at sea, resulting in various systems of flag signals; see, International maritime signal flags.
Use of flags outside of military or naval context begins only with the rise of nationalist sentiment by the end of the 18th century; the earliest national flags date to that period, and during the 19th century it became common for every sovereign state to introduce a national flag.