Cao lầu is a regional Vietnamese dish made with noodles, pork, and greens and is only found in the town of Hội An, in the Quang Nam Province of central Vietnam. Its unique taste is rumoured to be contributed by the water from an undisclosed ancient Cham well just outside of the town. This rumour is promulgated in a popular guide book and has become something of an urban legend. It is likely that the origin of Cao Lau in Hoi An goes back to the town's history as a trading port. Prior to the Chinese establishment in Hoi An, in the 17th century, the town was also a centre of Japanese trading activity. The famous Hoi An bridge also dates to this period. Cao Lau noodles are clearly derived from Japanese soba noodles. Although there are some who claim that they are Chinese wheat noodles, they are not made of wheat and have a different texture. There are as many variations on this dish as there are households in Hoi An. The noodles are Cao Lau; the way the pork is cooked (or omitted), the greens (the use or absence of mint), the use of lime or chilli jam, these are all variations on a theme. Use Cao Lau noodles and you have Cao Lau.