the passes of the high Himalayas. Dzongs were frequently built on a hilltop or mountain spur. If the dzong is built on the side of a valley wall, a smaller dzong or watchtower is typically built directly uphill from the main dzong with the purpose of keeping the slope clear of attackers who might otherwise shoot downward into the courtyard of the main dzong below (see image at head of article). Punakha Dzong is distinctive in that it is sited on a relatively flat spit of land at the confluence of the Mo and Pho Rivers. The rivers surround the dzong on three sides, providing protection from attack. This siting proved inauspicious, however, when in 1994 a glacial lake 90 kilometers upstream burst through its ice dam to cause a massive flood on the Pho Chhu, damaging the dzong and taking 23 lives. Construction By tradition, dzongs are constructed without the use of architectural plans. Instead construction proceeds under the direction of a high lama who establishes each dimension by means of spiritual inspiration. Dzongs are built using corvée labor applied as a tax against each household in the district. Under this obligation each family provides or hires a decreed number of workers to work for several months at a time (during quiet periods in the agricultural year) in the construction of the dzong. Dzongs comprise heavy masonry curtain walls surrounding one or more courtyards. The main functional spaces are usually arranged in two separate areas: the administrative offices; and the religious functions - including temples and monks' accommodation. This accommodation is arranged along the inside of the outer walls and often as a separate stone tower located centrally within the courtyard, housing the main temple, that can be used as an inner defensible citadel. The main internal structures are again built with stone (or as in domestic architecture by rammed clay blocks), and whitewashed inside and out, with a broad red ochre band at the top on the outside. The larger spaces such as the temple have massive internal timber columns and beams to create galleries around an open central full height area. Smaller structures are of elaborately carved and painted timber construction. The roofs are massively constructed in hardwood and bamboo, highly decorated at the eaves, and are constructed traditionally without the use of nails. They are open at the eaves to provide a ventilated storage area. They