Many of the known Hebrew names of the Kaifeng Jews were only found among Persian and Babylonian Jews. Jewish written sources do not mention how the Jews arrived in Kaifeng, though a legend says that they arrived by land on the Silk Road. Some Jesuit reports inaccurately stated the Kaifeng Jews did not intermarry. The Ming dynasty (1368–1644), in reaction to the foreign dynasty it replaced, laid down a policy of discrimination against foreigners, such as the resident Mongols and Semu. Laws regarding ethnic endogamy were issued that forbade members of such communities from marrying within their own groups. They were at liberty to marry only Han Chinese. Failure to do so would lead to enslavement. To what degree these measures were applied is unknown, but is evident from their Memorial Book that intermarriage took place on a large scale among the Kaifeng Jews certainly from Ming and it may be assumed, in Qing times. From the 19th century onwards it became the norm. They followed the Chinese custom of foot binding. The custom of the levirate marriage was retained, and polygamy was practiced: one Kaifeng Jew, the Zhang (張) clan's Zhang Mei, is recorded in the Memorial Book as having six wives, while Jin Rong-Zhang from the Jin clan (金) had five. Towards the end of the Ming period, calculations based on the community's memorial book suggest that the Kaifeng Jewish community amounted to some 4,000 people. The catastrophic flood of 1642 brought about a precipitous drop in their population, to around 1,000 souls. The flood also destroyed the synagogue. Considerable efforts were made to save the scriptures. One man of the Gao clan, Gao Xuan, dove repeatedly into the flooded synagogue to rescue what he could and afterward all seven clans helped restore and rewrite the 13 scrolls. They obtained some from Ningxia and Ningbo to replace them, and another Hebrew Torah scroll was bought from a Muslim in Ningqiangzhou (in Shaanxi), who acquired it from a dying Jew at Canton. Religious practices and beliefs When Kaifeng Jews introduced themselves to the Jesuits in 1605, they called themselves members of the house of "Israel" (一賜樂業:Yīcìlèyè) The Jesuits also noted that a Chinese exonym labelled them as Tiao jin jiao, "the sect that plucks the sinews" (挑筋教:Tiāojīn jiāo). This term arose from observing that, in memory of Jacob's wrestling with the angel, their butchers extracted the sciatic nerve (Gid