On a late Friday afternoon, Lamu men and boys in traditional Islamic dress sing before joining a procession to celebrate Maulidi, the Prophet Mohamed's birthday. Tambourines are played in mosques on the island but they are seldom used in Islamic culture elsewhere. Maulidi is a major event in Lamu attracting pilgrims from all over East Africa and sometimes farther afield. The celebrations last several days and each year, take place ten days earlier than the previous year's celebrations. Situated 150 miles north-northeast of Mombasa, Lamu town dates from the 15th century AD. The island's importance lies in the fact that it has the only certain source of sweet groundwater in the entire district. The town was declared a World Heritage Site by UNESCO in 2001 because it is the oldest and best preserved Swahili settlement in East Africa. Moreover, its architecture and urban development graphically demonstrates the diverse cultural influences that came together over many centuries to produce a distinctively local Swahili style and culture.