Bolesław I the Brave in 1025 he had himself crowned King of Poland. He was the first Polish ruler to receive the title of "rex" (Latin: "king"). He was an able administrator who established the "Prince's Law" and built many forts, churches, monasteries and bridges. He introduced the first Polish monetary unit, the "grzywna", divided into 240 "denarii", and minted his own coinage. Bolesław I is widely considered one of Poland's most capable and accomplished Piast rulers. Bolesław was born in 966 or 967, the first child of Mieszko I of Poland and his wife, the Bohemian princess Dobrawa. His "Epitaph", which was written
Mieszko I of Poland to the Warta River). In all probability Mieszko decided to pay tribute in order to avoid an invasion similar to the one that Lusatia had suffered. This homage would take place in 965, or in 966 at the latest. Very likely the tribute applied only to the Lubusz land, which was in the German sphere of influence. This understanding of the tribute issue explains why already in 967 Mieszko I was described in the Saxon chronicles as the Emperor's friend (or ally, supporter, Latin: "amicus imperatoris"). Probably in 964 Mieszko began negotiations with the Bohemian ruler Boleslav I the Cruel.