 Later he helped him to run the affairs of government and the sultanate, and co-signed an act of vassalage in 1560 - the oldest preserved Indonesian letter with seals.He is known in contemporary Portuguese sources as the heir to the throne ("herdeiro do reino"), though certain later sources say that he had one or two brothers with more legitimate claims.Ternate, an important center for the trade in cloves, had been heavily dependent on the Portuguese since 1522, when they built a stone fort on the island.