Regimental colours are the ceremonial flags of military regiments. Historically, their roots can be traced back at least as far as the Roman Empire. In many countries, regiments may have two colours, rather than one. One is called the king's colour or the national colour representing the military's loyalty towards a king or a nation, with a design typically based on the king's heraldic attributes or a national flag. The second colour is then designated the regimental colour representing the regiment itself. Countries which follow (or have historically followed) this system include Canada, Prussia, Poland, Spain, and the United Kingdom.