In April 1911, Albert Einstein was appointed as Professor of Theoretical Physics in the German section of Prague's Charles-Ferdinand University. He moved to Prague with his family, where he enjoyed walk across the Vltava river and around the historical city centre. Later that same year, he was invited to the first Solvay Congress, where he met Planck, Lorentz, Madame Curie, and Poincaré. While in Prague, Einstein began his systematic work on a relativistic theory of gravitation that paved the way for his general theory of relativity. Albert Einstein left Prague in July 1912 to take up a post at the Polytechnical Institute of Zurich. In 1923, he published the Czech edition of his popular book "About the Special and General Theory of Relativity in Plain Terms".