poetic history of The Brus and Wallace helped outline a narrative of united struggle against the English enemy. Arthurian literature differed from conventional version of the legend by treating Arthur as a villain and Mordred, the son of the king of the Picts, as a hero. The origin myth of the Scots, systematised by John of Fordun (c. 1320-c. 1384), traced their beginnings from the Greek prince Gathelus and his Egyptian wife Scota, allowing them to argue superiority over the English, who claimed their descent from the Trojans, who had been defeated by the Greeks. It was in this period that the national flag emerged as a common symbol. The image of St. Andrew martyred bound to an X-shaped cross first appeared in the Kingdom of Scotland during the reign of William I and was again depicted on seals used during the late 13th century; including on one particular example used by the Guardians of Scotland, dated 1286. Use of a simplified symbol associated with Saint Andrew, the saltire, has its origins in the late 14th century; the Parliament of Scotland decreed in 1385 that Scottish soldiers wear a white Saint Andrew's Cross on their person, both in front and behind, for the purpose of identification. Use of a blue background for the Saint Andrew's Cross is said to date from at least the 15th century. The earliest reference to the Saint Andrew's Cross as a flag is to be found in the Vienna Book of Hours, circa 1503. Like most western European monarchies, the Scottish crown in the fifteenth century adopted the example of the Burgundian court, through formality and elegance putting itself at the centre of culture and political life, defined with display, ritual and pageantry, reflected in elaborate new palaces and patronage of the arts. Renaissance ideas began to influence views on government, described as New or Renaissance monarchy, which emphasised the status and significance of the monarch. The Roman Law principle that "a king is emperor in his own kingdom" can be seen in Scotland from the mid-fifteenth century. In 1469 Parliament passed an act that declared that James III possessed "full jurisdiction and empire within his realm". From the 1480s the king's image on his silver groats showed him wearing a closed, arched, imperial crown, in place of the open circlet of medieval kings, probably the first coin image of its kind outside of Italy.