The title above translates to 13 Martyrs of Bagumbayan.
January 11, 1897 (7 days after the 15 martyrs' execution). Another execution was organized by the Spaniards as they were sentenced to death by musketry for collaborating with the anti-colonialism group Katipunan during the Filipino Revolution against Spain.
All of the martyrs executed on that day were Freemasons, most of them are part of the Katipunan, and members of the La Liga Filipina organized by Dr. Jose Rizal. The 13 martyrs were:
Numeriano Adriano
Domingo Franco
Moises Salvador
Francisco L. Roxas
Jose Dizon
Benedicto Nijaga
Geronimo Cristobal Medina
Antonio Salazar
Ramon A. Padilla
Faustino Villaruel
Braulio Rivera
Luis Inciso Villaruel
Estacio Manalac
A Historical Marker was placed in the fields within Luneta Park to honor the 13 Martyrs.
Sources:
Lead Image from http://katonynabanlawkasaysayan.blogspot.com/2014/01/january-11-13-martyrs-of-bagumbayan.html
http://www.philippinemasonry.org/the-13-martyrs-of-bagumbayan.html