Blood compact was an ancient treaty or covenant ritual signifying peace and friendship. In Spanish it is called Pacto de sangre; Sanduguan Filipino. Parties entering into a treaty would cut their wrists and pour their blood into a cup filled with liquid, such as wine, and drink the mixture.
On March 29, 1521, Ferdinand Magellan entered a treaty with Colambu, the rajah of Limasawa. According to Antonio Pigafetta, Magellan” had the king told through the slave that he desired to be casi casi with him, that is to say, brother.” Rajah Colambu responded in the affirmative saying that “he also wished to enter the same relations with the captain-general.”
Another blood compact was instituted between Miguel Lopez de Legazpi and Sicatuna of Bohol about the middle of March 1565.
When Magellan reached Cebu on April 7, 1521, Rajah Humabon demanded that he should pay tribute. But Magellan refused and told him that he would destroy him like what he did to Calicut and Malaca. Rajah Humabon replied that he would deliberate with his men and will give them his decision the following day. So, on April 8, 1521, Magellan and Rajah Humabon agreed to commence the rite of blood compact.
Below is an excerpt from Pigafetta’s First Voyage Around the World:
Monday morning, our notary, together with the interpreter, went to Zubu. The king, accompanied by his chiefs, came to the open square where he had our men sit down near him. He asked the notary whether there were more than one captain in that company, and whether that captain wished him to pay tribute to the emperor his master. The notary replied in the negative, but that the captain wished only to trade with him and with no others. The king said that he was satisfied, and that if the captain wished to become his friend, he should send him a drop of blood from his right arm, and he himself would do the same [to him] as a sign of the most sincere friendship. The notary answered that the captain would do it. Thereupon, the king told him that all the captains who came to that place, were wont to give presents one to the other [i.e., mutual presents between the king and the captain], and asked whether our captain or he ought to commence. The interpreter told the king that since he desired to maintain the custom, he should commence, and so he did.http://www.gutenberg.org
http://www.gutenberg.org. The Philippine Islands, Volume XXXIII.