It was in the middle of this final struggle, and when the result might still be held doubtful, that Tsin Chi Hwangti began his eventful reign. When he began to rule he was only thirteen years of age, but he quickly showed that he possessed the instinct of a statesman, and the courage of a born commander of armies. On the one hand he sowed dissension between the most formidable of his opponents, and brought about by a stratagem the disgrace of the ablest general in their service, and on the other he increased his army in numbers and efficiency, until it became unquestionably the most formidable fighting force in China. While he endeavored thus to attain internal peace, he was also studious in providing for the general security of the empire, and with this object he began the construction of a fortified wall across the northern frontier to serve as a defense against the troublesome Hiongnou tribes, who are identified with the Huns of Attila. This wall, which he began in the first years of his reign, was finished before his death, and still exists as the Great Wall of China, which has been considered one of the wonders of the world. He was careful in his many wars with the tribes of Mongolia not to allow himself to be drawn far from his own border, and at the close of a campaign he always withdrew his troops behind the Great Wall. Toward Central Asia he was more enterprising, and one of his best generals, Moungtien, crossed what is now the Gobi Desert, and made Hami the frontier fortress of the empire.