Since Fiji spans  from east to west, it has been a nation of many languages. Fiji has long had permanent settlements, but its peoples also have a history of mobility. Over the centuries, unique Fijian cultural practices developed. Fijians constructed large, elegant watercraft, with rigged sails called ''drua'' and exported some of to Tonga. Fijians also developed a distinctive style of village architecture, including of communal and individual ''bure'' and ''vale'' housing, and an advanced system of ramparts and moats that were usually constructed around the more important settlements. Pigs were domesticated for food, and a variety of agricultural plantations, such as banana plantations, existed from an early stage. Villages were supplied with water brought in by constructed wooden aqueducts. Fijians lived in societies led by chiefs, elders and notable warriors. Spiritual leaders, often called ''bete'', were also important cultural figures, and the production and consumption of ''yaqona'' was part of their ceremonial and community rites. Fijians developed a monetary system where the polished teeth of the sperm whale, called ''tambua'', became an active currency. A type of writing existed which can be seen today in various petroglyphs around the islands. Fijians developed a refined ''masi'' cloth textile industry, and used the cloth they produced to make sails and clothes such as the ''malo'' and the ''liku''. As with most other ancient human civilisations, warfare or preparation for warfare was an important part of everyday life in pre-colonial Fiji. The Fijians were noted for their distinctive use of weapons, especially war clubs. Fijians use many different types of clubs that can be broadly divided into two groups, two handed clubs and small specialised throwing clubs called ''ula''.