Many flags include symbols that are used to express ideas which would otherwise take many words. These symbols derive from many different sources - from animals to plants, weapons to everyday objects. One of the best-known examples is the lion in medieval heraldry, which represented both kingship and bravery. Colours are also given symbolic meanings. Red once stood for courage, nobility, and power; today it has become the colour of 'people power' when used in flags like those of the Soviet Union and China. We use white and blue to represent peace in flags like that of the United Nations. Green is the colour of vegetation, but has also been used to represent youth and hope. Religious ideas are among the oldest to be expressed in flag form and the cross is the oldest device in heraldry. In Moslem countries the crescent moon has been a symbol of religion since at least the fourteenth century, although the crescent combined with a star is not so old. Another Islamic symbol  is the double-bladed sword, which represents the Prophet's son-in-law, Ali. Islamic law does not allow the depiction of God or people, but other countries have no such restrictions and there are many Chinese flags that show images of saints. Modern symbols include the Canadian maple leaf.