In the years 1225-1226, Duke Konrad Mazowiecki held talks with the Teutonic Order. He offered the knights a fief in the form of Chelmno Land, and in return, he asked for the protection of his border with pagan Prussia. Konrad Mazowiecki managed to make a deal with the Teutonic Knights. He did not know that the monks had their own secret colonization plans toward his lands, and above all toward Prussia. Meanwhile, Grand Master Hermann von Salza asked Emperor Frederick II for the so-called Golden Bull of Rimini – a document allegedly issued in 1226 that gave the Teutonic Knights the rights to all lands they would acquire in Prussia. The emperor issued it, calling himself a senior of the order, and also a completely unjustified senior of Poland.
Today, historians believe that the bull was not really written until 1234 and was backdated. The monks also sought grants from the Pope, who declared Prussia the property of St. Peter and considered his fief.
The first monastic brothers, two knights, and a dozen servants were sent by Hermann von Salza to the Chelmno Land in 1228, the next knights arrived two years later. A small Teutonic branch, commanded by Herman Balek, started the hostilities moving along the Vistula, crossed it, and built a small stronghold, the watchtower of which, according to a legend upheld by the Teutonic Knights, was located on the branches of a huge oak. These were the beginnings of the stronghold in Torun. In the following years, new castles were built to control the conquered areas and were the basis for further forays: Chelmno, Kwidzyn, Elblag.
The Prussians were defeated in the fight against the Order, the conquest of their country ended around 1238 and from that time the Teutonic Knights began to give concerts in the lands of Sambia and Samogitia, as well as Lithuania and Poland. After the fall of the besieged Akka, the Teutonic Knights stayed in Venice for a short time, in 1308 Grand Master Siegfried von Feuchtwangen moved the capital of the monastic state from Venice to Malbork. As the state of Jerusalem weakened, the Prussian power of the order grew.