Foreign maritime trade in China was regulated through the Canton System, which emerged gradually through a series of imperial edicts in the 17th and 18th centuries. This system channeled formal trade through the "Cohong", a guild of thirteen trading companies (known in Cantonese as "hong") selected by the imperial government. In 1725, the Yongzheng Emperor gave the "Cohong" legal responsibility over commerce in Guangzhou. By the 18th century, Guangzhou, known as Canton to British merchants at the time, had become the most active port in the China trade, thanks partly to its convenient access to the Pearl River Delta. In 1757, the Qianlong Emperor confined all foreign maritime trade to Guangzhou. Qianlong, who ruled the Qing dynasty at its zenith, was wary of the transformations of Chinese society that might result from unrestricted foreign access. Chinese subjects were not permitted to teach the Chinese language to foreigners, and European traders were forbidden to bring women into China.