The terraces are the only form of stone construction from the pre-colonial period. The Philippines alone among south-east Asian cultures is a wholly wood-based one: unlike Cambodia, Indonesia, or Thailand, in the Philippines both domestic buildings and ritual structures such as temples and shrines were built from wood, a tradition that has survived in the terrace hamlets. Terracing began in the Cordilleras some 2,000 years ago, although scholars disagree about its original purpose. It is evidence of a high level of knowledge of structural and hydraulic engineering on the part of those who built the terraces. The knowledges and practices, supported by rituals, involved in maintaining the terraces are transferred orally from generation to generation, without written records. Taro was the first crop when they began to be used for agriculture, later to be replaced by rice, which is the predominant crop today.