of decline compounded by internal strife over royal succession. Piracy was also detrimental to the kingdom. Spain declared war in 1578, attacking and capturing Brunei’s capital at the time, Kota Batu. This was achieved as a result in part of the assistance rendered to them by two Bruneian noblemen, Pengiran Seri Lela and Pengiran Seri Ratna. The former had travelled to Manila to offer Brunei as a tributary of Spain for help to recover the throne usurped by his brother, Saiful Rijal. The Spanish agreed that if they succeeded in conquering Brunei, Pengiran Seri Lela would indeed become the Sultan, while Pengiran Seri Ratna would be the new Bendahara. In March 1578, the Spanish fleet, led by De Sande himself, acting as Capitán-General, started their journey towards Brunei. The expedition consisted of 400 Spaniards, 1,500 Filipino natives and 300 Borneans. The campaign was one of many, which also included action in Mindanao and Sulu.
The Spanish succeeded in invading the capital on 16 April 1578, with the help of Pengiran Seri Lela and Pengiran Seri Ratna. The Sultan Saiful Rijal and Paduka Seri Begawan Sultan Abdul Kahar were forced to flee to Meragang then to Jerudong. In Jerudong, they made plans to chase the conquering army away from Brunei. The Spanish suffered heavy losses due to a cholera or dysentery outbreak. They were so weakened by the illness that they decided to abandon Brunei to return to Manila on 26 June 1578, after just 72 days. Before doing so, they burned the mosque, a high structure with a five-tier roof.
Pengiran Seri Lela died in August–September 1578, probably from the same illness that had afflicted his Spanish allies, although there was suspicion he could have been poisoned by the ruling Sultan. Seri Lela's daughter left with the Spanish and went on to marry a Christian Tagalog, named Agustín de Legazpi de Tondo.
The local Brunei accounts differ greatly from the generally accepted view of events. The Castilian War
