attacked Simtokha Dzong. Equipped with large numbers of matchlocks as well as Chinese trebuchets, Karma Tenkyong's troops quickly stormed the palace. The Tibetans went on to demand hostages from Ngawang Namgyal, who only gave a defiant reply. While Tibetan soldiers were looting the dzong, however, its gunpowder stores were ignited, perhaps by accident. Simtokha Dzong, constructed just three years prior, exploded, killing most of the Tibetan forces present. As the Tibetans had been unaware of the ammunition, with the explosion seemingly coming out of nowhere, panic quickly spread among the survivors. Recognizing the chance, Zhabdrung's forces managed to overwhelm the remaining Tibetans in a counterattack. Bhutanese sources even claim that "the few [invaders] who survived, returned to Tibet with the news of a terrible defeat." Ardussi argues, however, that "it [is not] certain that the dispersal of the Tibetan and allied Bhutanese armies was complete" and that sporadic fighting in western Bhutan probably continued until 1639. After their victory at Simtokha Dzong, Ngawang Namgyal and his followers also expelled the Barawa monks from their strongholds in the Gasa valley, eliminating one rival sect from Bhutan for good. Aftermath Even though his forces had triumphed over the Tibetan invaders and he remained in power, Ngawang Namgyal's victory was a costly one. His regime had almost collapsed and his new seat of power was destroyed, while both the Tsangpa dynasty and the rival lamas remained a constant threat to his realm. Nevertheless, Ngawang Namgyal resumed "with undiminished determination to carry on his task of state-building". After praying for the fallen soldiers at Chagri Monastery, he immediately began to seek a place to construct an even grander dzong than Simtokha. After he found one, the foundation for the new Punakha Dzong was laid in 1637; after its completion it remained the administrative centre and the seat of the Government of Bhutan until 1955, when the capital was moved to Thimphu. Simtokha Dzong, on the other hand, was only rebuilt in 1671. While Ngawang Namgyal continued to unify Bhutan, the Tibetans and their dissident Bhutanese allies launched one last invasion in 1639, but this war quickly turned into a stalemate. Meanwhile, the Tsangpa were increasingly confronted with conflicts in Tibet, so that Karma Tenkyong eventually initiated negotiations to end the conflict. Zhabdrung Rinpoche Ngawang Namgyal was recognized by the Tibetans as ruler of western Bhutan, and in the years until his death he would