Almost the only form of unity which Germans possessed in the eighteenth century was that of language and culture, and even this was no strong bond. It was not an easy matter for Germans to understand each other's dialects. Since Luther's day the written language had been more stable. Lessing may perhaps be regarded as the first of the modem German dramatists and critics, and by 1790 Germany was on the eve of her great age of literary achievement. The influence of French culture in Germany was very strong in the eighteenth century. Frederick the Great himself normally spoke and wrote in French. He was proud to have Voltaire at his court. His palace and grounds at Sans Souci were modelled on Versailles. Germany had no religious unity such as Catholic France and Protestant England possessed, for North Germany was Protestant; Austria, South Germany, the Rhineland and Silesia were predominantly Catholic.