Bishop Christian asked the new Pope Honorius III for the consent to start another Crusade, however a first campaign in 1217 proved a failure and even the joint efforts by Duke Konrad with the Polish High Duke Leszek I the White and Duke Henry I the Bearded of Silesia in 122 / 23 only led to the reconquest of Chełmno Land but did not stop the Prussian invasions.

At least Christian was able to establish the Diocese of Chełmno east of the Vistula, adopting the episcopal rights from the Masovian Bishop of Płock, confirmed by both Duke Konrad and the Pope.

Duke Konrad of Masovia still was not capable to end the Prussian attacks on his territory and in 1224 began to conduct negotiations with the Teutonic Knights under Grand Master Hermann von Salza in order to strengthen his forces.

He obtained a charter by Emperor Frederick II issued in the 1226 Golden Bull of Rimini, whereby Chełmno Land would be the unshared possession of the Teutonic Knights, which was confirmed by Duke Konrad of Masovia in the 1230 Treaty of Kruszwica.

In 1226 Duke Konrad I of Masovia summoned the Teutonic Knights for assistance ; by 1230 they had secured Chełmno ( Culm ) and begun claiming conquered territories for themselves under the authority of the Holy Roman Empire, although these claims were rejected by the Poles, whose ambition had been to conquer Prussia all along.

Also, the Teutonic Knights were invited to Prussia by Duke Konrad of Masovia to Christianise the Prussians in 1226.

In 1229 he was captured and arrested at Płock Castle by rivaling Duke Konrad I of Masovia.

Konrad I, the Polish Duke of Masovia, unsuccessfully attempted to conquer pagan Prussia in crusades in 1219 and 1222.

In 1225 Duke Konrad I of Masovia asked the Teutonic Knights to protect his territory from such raids.

After a number of years Duke Konrad I of Masovia invited the Teutonic Knights to Christianize the pagan Prussians in 1226.

The order of march of the German army was as follows: the three Bavarian contingents, the Frankish contingent under Duke Konrad, the royal unit ( the center ), the two contingents of Swabians and the Bohemian contingent.

Henry IV was the only son of Duke Henry III the White of Silesia-Wrocław by his first wife Judith, daughter of Duke Konrad I of Masovia.

* February 14 – Konrad VII the White, Duke of Oleśnica

The second time happened two years later, when Henry the Bearded was captured by Duke Konrad I of Masovia.

However, the will was ignored by Duke Konrad of Masovia and Władysław's III nephew Władysław Odonic.

Upon the invitation of Duke Konrad I of Masovia, the Teutonic Knights took possession of Prussia in the 13th century and created a monastic state to administer the conquered Old Prussians.

Freiburg was founded by Konrad and Duke Bertold III of Zähringen in 1120 as a free market town ; hence its name, which translates to " free ( or independent ) town ".

The first well organised mercenaries in Italy were the Ventura Companies of Duke Werner von Urslingen and Count Konrad von Landau.

In the course of the fragmentation under Duke Bolesław II the Bald and his younger brother, the Duchy of Głogów under Duke Konrad I was established in 1251.

Philip's father-in-law George, Duke of Saxony, the bishop of Würzburg, Konrad II von Thungen, and the archbishop of Mainz, Albert III of Brandenburg, were active in agitating against the growth of the Reformation.

* 1713 – Charles I, Duke of Brunswick-Wolfenbüttel ( d. 1780 )

* 1557 – Frederick I, Duke of Württemberg ( d. 1608 )

* Albert I, Duke of Brunswick-Lüneburg ( 1236 – 1279 ) second Duke of Brunswick-Lüneburg

* Albert I, Duke of Prussia ( 1490 – 1568 ), first Duke of Prussia

Albert the Bear (; c. 1100 – 18 November 1170 ) was the first Margrave of Brandenburg ( as Albert I ) from 1157 to his death and was briefly Duke of Saxony between 1138 and 1142.

Albert was a loyal vassal of his relation, Lothar I, Duke of Saxony, from whom, about 1123, he received the Margraviate of Lusatia, to the east ; after Lothar became King of the Germans, he accompanied him on a disastrous expedition to Bohemia in 1126, when he suffered a short imprisonment.

Albert was chosen as his successor early in 1511 in the hope that his relationship to his maternal uncle, Sigismund I the Old, Grand Duke of Lithuania and King of Poland, would facilitate a settlement of the disputes over eastern Prussia, which had been held by the Order under Polish suzerainty since the Second Peace of Thorn ( 1466 ).

He married secondly to Anna Maria ( 1532 – 20 March 1568 ), daughter of Eric I, Duke of Brunswick-Lüneburg, in 1550.

He was elected Grand Duke of Lithuania on the death of his father ( 1492 ), and King of Poland on the death of his brother John I Albert ( 1501 ).

By the age of twenty, Ferdinando I, Duke of Mantua, began commissioning works from him, and he was also employed by local jewelers for figurative designs.

* Afonso, 1st Duke of Braganza, son of John I of Portugal.

* Afonso, Duke of Porto, son of Louis I of Portugal.

* Alfonso I d ' Este, Duke of Ferrara during the time of the War of the League of Cambrai.

* Alfonso I d ' Este, Duke of Ferrara ( 1476 – 1534 )

In the summer of 1214, Andrew had a meeting with Grand Duke Leszek I of Poland and they agreed that they would divide the Principality of Halych between Hungary and Poland.

However, Andrew denied to transfer the agreed territories to Duke Leszek I who made an alliance with Prince Mstilav of Novgorod and they drove away Andrew's troops from the principality.

Andronikos III was first married, in 1318, with Irene of Brunswick, daughter of Henry I, Duke of Brunswick-Lüneburg ; she died in 1324.

This provision was repealed in 1716, at the request of George I, who was also the Elector of Hanover and Duke of Brunswick-Lüneburg of the Holy Roman Empire, and so frequently needed and wanted to stay in Hanover.

* 1578 – Duel of the Mignons claims the lives of two favourites of Henry III of France and two favorites of Henry I, Duke of Guise.

* 1290 – Leopold I, Duke of Austria ( d. 1326 )

* 1574 – Cosimo I de ' Medici, Grand Duke of Tuscany ( b. 1519 )

An accord was made between him and the Bohemian Duke Borivoj I ( reigned 870-95 ); Bohemia was thus freed from the dangers of invasion.

In 1600 he was called to Parma by Duke Ranuccio I Farnese to began the decoration of the Palazzo del Giardino, but he died before it was finished.