As a part of Maulidi, Lamu Island's celebrations to mark the birthday of the Prophet Mohamed, a keenly-fought boat race is held. Maulidi is a joyous event in Lamu and attracts 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. The boat race is a battle between the crews of the wooden sailing boats of the region, called mashua, which more commonly known to visitors as dhows. Each boat has a crew of up to twelve. The approach to the first marker buoy is always a time of heightened tension.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.