The discovery of gunpowder rendered the medieval fortifications unnecessary. A prestigous appearance and comfortable living now did more for the reputation of the owner than sturdy walls and high towers. For this very reason, Joachim II. wanted to transform his medieval castle into an impressive renaissance palace with a demonstrative new building, and thus build for himself a permanent residence that could compete with the seats of government in the neighbouring feudal states that were beginning to make names for themselves (for example in Dresden and Torgau).
He began in 1536 with the transfer of the cathedral diocese to the Dominican church – the preaching monks relocated to Brandenburg - and had the remains of his ancestors transported from the Lehnin monastery to the cathedral church. And so he pointed the way – Berlin became his proper residence.
With the arrival of the Reformation from 1539, the sovereign acquired the religious fiefs (land and estates). The wealth that he gained in this way made possible the rebuilding of the electoral castle – something that had already been decided upon for a long time. As early as 1537, the architect of Torgau Palace, Konrad (Kunz) Krebs (1492 – 1540) is said to have, during a stay in Berlin, drawn up various plans for a new Berlin palace, so that afterwards a wooden model could be built in Torgau. Following his premature death in 1540, his apprentice Caspar Theiss (died 1550) became the architect of the new palace. The rebuild began in 1537/38 with the banqueting hall wing on the city side, and when it was completed in 1540, the build continued with the living quarters wing on the Spree side.