ancient India sea power. It played a vital role in the expansion of the empire, including the conquest of the Ceylon islands and naval raids on Srivijaya. The navy grew both in size and status during the medieval Cholas reign. The Chola admirals commanded much respect and prestige. The navy commanders also acted as diplomats in some instances. From 900 to 1100, the navy had grown from a small backwater entity to that of a potent power projection and diplomatic symbol in all of Asia, but was gradually reduced in significance when the Cholas fought land battles subjugating the Chalukyas of the Andhra-Kannada area in South India. A martial art called Silambam was patronised by the Chola rulers. Ancient and medieval Tamil texts mention different forms of martial traditions but the ultimate expression of the loyalty of the warrior to his commander was a form of martial suicide called Navakandam. The medieval Kalingathu Parani text, which celebrates the victory of Kulothunga Chola I and his general in the battle for Kalinga, describes the practice in detail. Economy Land revenue and trade tax were the main source of income. The Chola rulers issued their coins in gold, silver and copper. The Chola economy was based on three tiers—at the local level, agricultural settlements formed the foundation to commercial towns nagaram, which acted as redistribution centres for externally produced items bound for consumption in the local economy and as sources of products made by nagaram artisans for the international trade. At the top of this economic pyramid were the elite merchant groups (samayam) who organised and dominated the regions international maritime trade. One of the main articles which were exported to foreign countries were cotton cloth. Uraiyur, the capital of the early Chola rulers, was a famous centre for cotton textiles which were praised by Tamil poets. The Chola rulers actively encouraged the weaving industry and derived revenue from it. During this period the weavers started to organise themselves into guilds. The weavers had their own residential sector in all towns. The most important weaving communities in early medieval times were the Saliyar and Kaikolar. During the Chola period silk weaving attained a high degree and Kanchipuram became one of the main centres for silk. Metal crafts reached its zenith during the 10th to 11th centuries because the Chola rulers like Chembian Maadevi extended their patronage to metal craftsmen. Wootz steel was