Casimir I the Restorer (Kazimierz I Odnowiciel; 25 July 1016 – 28 November 1058), was a Duke of Poland of the Piast dynasty and the de facto monarch of the entire country. He is known as the Restorer mostly because he managed to reunite all parts of the Polish Kingdom after a period of turmoil. He reinstated Masovia, Silesia and Pomerania into his realm. Son of Mieszko II Lambert and Richensa of Lotharingia, Casimir failed to crown himself the King of Poland, mainly because of internal and external threats to his rule.
Relatively little is known of Casimir's early life. Born to Mieszko II of Poland and Richensa of Lotharingia, the granddaughter of Emperor Otto II, he must have spent his childhood at the royal court of Poland in Gniezno. Casimir seems to have been destined for the cloth as he was sent away to monastery in 1026. He left the church, however, in 1031.
Casimir's father Mieszko II was crowned the king of Poland in 1025 after the death of Boleslaw I Chrobry. However, powerful magnates feared a strong central government reminiscent of Boleslaw's rule. This situation led to considerable friction between crown and nobility. Taking advantage of the king's precarious situation, Mieszko's brothers Bezprym and Otton turned against him and allied themselves with Emperor Conrad II whose forces attacked the country, regaining Lusatia. Years of chaos and conflict followed, during which Mieszko II died (A.D. 1034) in suspicious circumstances after he was forced to abdicate. Following his fathers death Casimir attempted to seize the throne in 1034. This precipitated a Barons rebellion, which coupled with the so called "Pagan Reaction" of the commoners forced Casimir to flee to Saxony (A.D. 1034). Casimir returned to Poland and in 1038, once again, tried to regain power with the aide of his influential mother. This also failed and Casimir had to flee to the Kingdom of Hungary where he was imprisoned by Stephen I.
The central parts of Poland were controlled by Bezprym. The central district of Wielkopolska revolted against the nobles and catholic clergy in a mass rebellion.pagan revival ensued there for some years. The district of Masovia seceded and a local landlord named Miecław formed a state of his own there. A similar situation took place in Pomerania. Taking advantage of the chaos and his neighbour's weakness, Duke Bretislaus I of Bohemia, invaded and revaged the country. After a short struggle Bretislaus I gained control of Silesia, took Małopolska along with Cracow and severely pillaged Greater Poland, burning Gniezno to the ground and looting the relics of Saint Adalbert. Greater Poland was in fact razed so completely that it ceased to function as a primary power base of the Polish kingdom.
The following year the new Holy Roman Emperor, Henry III, allied himself with the exiled Polish ruler against the Bohemians. Casimir was given a troop of 1,000 heavy footmen and a significant amount of gold to restore his power in the country. Casimir also signed an alliance with Yaroslav I the Wise, the Prince of Kievan Rus'. The alliance was sealed by Casimir's marriage with Yaroslav's sister, Maria Dobronega. With such support Casimir returned to Poland and managed to retake most of his domain. In 1041, the defeated Bretislaus signed a treaty at Regensburg in which he renounced his claims to all Polish lands except for Silesia, which was to be incorporated into the Crown of Bohemia. It was Casimir's success in strengthening royal power and ending internal strife that earned him the epithet of "the Restorer".
The treaty gained Casimir a period of peace at the southern border and the capital of Poland was moved to Kraków, the only major Polish city relatively untouched by the wars. It is probable that the Holy Roman Emperor was happy with the balance of power restored in the region and forced Casimir not to crown himself the king of Poland. In 1046 Emperor Henry held royal and imperial courts at Merseburg and Meissen, at which he ended the strife among the Dux Bomeraniorum (Duke of Pomerania), Duke Bretislaus of Bohemia, and Poland's Casimir I. In 1047 Casimir, aided by his Kievan ally, started a war against Masovia and seized the land. It is probable that he also defeated Miecław's allies from Pomerania and attached Gdańsk to Poland. This secured his power in central Poland. Three years later, against the will of the emperor, Casimir seized Bohemian-controlled Silesia, thus securing most of his father's domain. In 1054 in Quedlinburg the Emperor ruled that Silesia was to remain in Poland in exchange for a yearly tribute of 117 kilograms of silver and 7 kg of gold.
At that time Casimir focused on internal matters. Conflicted with the Emperor in the Silesian case, he supported the Papacy in the Investiture Controversy and gained the support of the church. To strengthen his rule he re-created the bishopric in Kraków and Wrocław and erected the new Wawel Cathedral. During Casimir's rule heraldry was introduced in Poland and, unlike his predecessors, he promoted landed gentry over the drużyna as his base of power. One of his reforms was the introduction, to Poland, of a key element of feudalism: the granting of fiefdoms to his retinue of warriors, thus gradually transforming them into medieval knights.