In 1665 the Anhalt-Köthen branch became extinct, and according to a family compact, this district was inherited by Lebrecht, Prince of Anhalt-Plötzkau, who surrendered Plötzkau to Bernburg and took the title of prince of Anhalt-Köthen. In the same year the princes of Anhalt decided that if any branch of the family became extinct its lands should be equally divided among the remaining branches. This arrangement was carried out after the death of Frederick Augustus, Prince of Anhalt-Zerbst, in 1793, and Zerbst was divided between the three remaining princes. During these years the policy of the different princes was marked, perhaps intentionally, by considerable uniformity. Once or twice Calvinism was favoured by one of the princes, but in general, the house was loyal to the doctrines of Martin Luther. The growth of Prussia provided Anhalt with a formidable neighbour, and the establishment and practice of primogeniture by all branches of the family prevented the further division of the principality.