The preparatory course of study extended over some twenty years. The Brehon laws were originally composed in poetic verse to aid memorisation. Brehons were liable for damages if their rulings were incorrect, illegal or unjust. When one brehon had adjudicated on a matter submitted to him, there could be no appeal to another brehon of the same rank; but there might be an appeal to a higher court, provided the appellant gave security. The ranking of a brithem was based on his skill, and on whether he knew all three components of law: traditional law, poetry, and (added later) canon law.