Four years later, in 1725, Philip Johan von Strahlenberg was the first to depart from the classical Don boundary by proposing that mountain ranges could be included as boundaries between continents whenever there were deemed to be no suitable waterways, the Ob and Irtysh Rivers notwithstanding. He drew a new line along the Volga, following the Volga north until the Samara Bend, along Obshchy Syrt (the drainage divide between Volga and Ural) and then north along Ural Mountains. This was endorsed by the Russian Empire, and introduced the convention that would eventually become commonly accepted, but not without criticism by many modern analytical geographers like Halford Mackinder who saw little validity in the Ural Mountains as a boundary between continents.