The red dragon of Wales dates back to Roman times. Roman cavalry units carried a standard known as the ‘draco’, or dragon. This took the form of a metal dragon’s head with an open mouth, through which the wind would blow.
The body of the dragon was made up of a tube of fabric, rather like a modern wind sock. The banners were used to serve as markers on which the riders formed into different formations, and to give orders by means of some vigorous waving.
The British militias adopted many aspects of Roman military gear, and the impressive looking draco was among those taken up.
Following the fall of Rome, British princes continued to use Roman-style dracos as battle standards. The last recorded use of the draco by a British army wasn’t until about 1250, after which the red dragon of Wales began to be embroidered onto a flag as if it were a heraldic device.
The green and white background, incidentally, comes from the family colours of the Tudor Dynasty and was added in 1959.
Answered by one of our Q&A experts, Rupert Matthews