This Nerchinsk Treaty, exacted literally at the cannon's mouth, was not only the first concluded between China and Russia, but the first between China and any foreign Power. It was essentially a boundary treaty, though free trade between the two countries was also provided for ; yet the Chinese made the fatal mistake of leaving the eastern frontier, beyond the line of the Ussuri, for future definition, their only excuse being ignorance of the country ; though the Ming Emperors Hun-wu (1368-98) and Yun-lo, in 1413, had sent expeditions to the lower Amoor ; built temples there ; and erected stone monuments, with inscriptions, that still exist.