Theoretical obligations between a samurai and his lord (usually a daimyo) increased from the Genpei era to the Edo era. They were strongly emphasized by the teachings of Confucius and Mencius (ca 550 BC), which were required reading for the educated samurai class. Bushido was formalized by several influential leaders and families before the Edo Period. Bushido was an ideal, and it remained fairly uniform from the 13th century to the 19th century — the ideals of Bushido transcended social class, time and geographic location of the warrior class.