Oslob has always been frequented by Muslim slave raiders but in 1813, with the aid of Fray Julian Bermejo’s string of watchtowers, the local armed militia was able to repel and capture the leader of a raiding party off Sumilon Island. This decisive event led to the formation of a new town that is now the current poblacion of Oslob. Prior to that and located around two kilometers south, are the ruins of a former fortified settlement called Daanglungsod.
The Muslim slave raids in the middle of the 18th to the middle of the 19th centuries were indeed one of the darkest years of colonial Philippines. It is estimated that during this period, around 200,000 natives were abducted. Because of the ineffectiveness and lack of political will of the governing colonial power to stem these raids, and prior to 1848, the navy vessels were often outrun by the faster prahus, or, in the case of Bicol, refused the request of the mayors to arm their towns for fear that the townspeople will revolt against them, these depradations dragged on for more than a hundred years.
The pirate wind, locally called the habagat or the southwest monsoon blows between May and October. It intensifies in August and September of which the Ilanun (or Iranun or Lanun) and later, the Balangingi (Iranun and their captives who were integrated into their community living in the island of Balangingi) took advantage. These were the months that communities across Southeast Asia were afraid of.