The domestic order and tranquillity of the kingdom had been restored by his painstaking father, but Poland had shrunk territorially since the age of his grandfather Boleslaus I., and it was the aim of Boleslaus II.
Anxious to regain these lands Henry allied himself with some Slavonic tribes, promising not to interfere with the exercise of their heathen religion, while Boleslaus found supporters among the discontented German nobles.
On the 26th of December 1076 Boleslaus encircled his own brows with the royal diadem, a striking proof that the Polish kings did not even yet consider their title quite secure.
In 1069 he succeeded in placing Izaslaus on the throne of Kiev, thereby confirming Poland's overlordship over Russia and enabling Boleslaus to chastise his other enemies, Bohemia among them, with the co-operation of his Russian auxiliaries.
The obstinacy of the resistance convinced Boleslaus that Pomerania must be christianized before it could be completely subdued; and this important work was partially accomplished by St Otto, bishop of Bamberg, an old friend of Boleslaus's father, who knew the Slavonic languages.
Here also are conserved the remains of St Stanislaus, the patron saint of the Poles, who, as bishop of Cracow, was slain before the altar by King Boleslaus in 1079.
So magnificently that the emperor, declaring such a man too worthy to be merely princess, conferred upon him the royal crown, though twenty-five years later, in the last year of his life, Boleslaus thought it necessary to crown himself king a second time.
Unlike the people of other Slavonic countries, the Poles are comparatively poor in popular and legendary poetry, but such compositions undoubtedly existed in early times, as may be seen by the writings of their chroniclers; thus Gallus translated into Latin a poem written on Boleslaus the Brave, and a few old Polish songs are included in Wojcicki's Library of Ancient Writers.
The honors of the ensuing war were with Henry, and when peace was made in 1006 Boleslaus gave up Bohemia, but the struggle was soon renewed and neither side had gained any serious advantage when peace was again made in 1013.
The death of Boleslaus in 1025, and a cession of some lands north of the Eider to Canute, king of Denmark and England, secured the northern and eastern frontiers of Germany from attack, and the king's domestic enemies were soon crushed.