kings of Toungoo and Chiang Mai also revolted. Another key viceroy, Nyaungyan of Ava nominally stayed loyal but offered no support. Instead, Nyaungyan consolidated his position in Upper Burma throughout 1597. More chaos ensued. In September 1597, the rebellious Mingyi Hnaung of Prome was assassinated. Toungoo tried to pick off Prome but failed. Toungoo then formed an alliance with Arakan to attack Pegu. Combined Arakan and Toungoo forces laid siege to Pegu in April 1599. Nanda surrendered on 19 December 1599. The victors looted all the gold, silver and valuables that had been collected in the last 60 years by Tabinshwehti and Bayinnaung. Before they left in late February 1600, the Arakanese burned down the city, including Bayinnaung's once-glittering Grand Palace. When Naresuan and his Siamese army showed up at Pegu to join the free-for-all, they found a smoldering city with the loot already taken away. Naresuan hastily followed up to Toungoo, laying siege to the city in April 1600. But his supply lines were cut by the Arakanese from the rear, forcing the Siamese king to withdraw on 6 May 1600. The Siamese forces suffered heavy losses in retreat. Only a small portion finally got back to Martaban. It was the last time the Siamese ever invaded mainland Burma. After the 1600 debacle, Naresuan turned north to Lan Na. In early 1602, King Nawrahta Minsaw of Lan Na who was facing attacks from Lan Xang agreed to become a Siamese tributary. Arakan At the beginning of the 17th century, Arakan was at the height of its powers. Its dominion extended across a thousand miles of coastline from Chittagong to Syriam. In the previous century, the Arakanese with the help of Portuguese mercenaries had extended their grip of the trade through the Arakanese littoral up to Chittagong. It had grown wealthy from trade, including trade in slaves, which it actively raided from the Ganges delta. Portuguese insurrections But its success depended greatly on the use of Portuguese mercenaries who proved unreliable and troublesome. Arakan lost the port city of Syriam in Lower Burma in 1603 when its Portuguese governor Filipe de Brito e Nicote declared that he was now loyal to the Portuguese viceroy of Goa. After two failed expeditions by the Arakanese navy to retake the port in 1604 and 1605, Arakan gave up its claims on the Lower Burma coastline. Arakan's Portuguese troubles were not yet over. In