Oral tradition traces the roots of Gumaca to the 14th century when it was settled by Borneans and Malays who established a village at the southern bank of the Palanas River. It earliest ruler said to be Lakan Bugtali extended his rule to encompass the present town of Calauag to the southwest, Gamao Point to the north, Kalilayan River to the northeast and to Alabat Island across Lamon Bay (formerly Gusuan).
Gumaca, writes Juan Álvarez Guerra in Viajes por Filipinas: De Manila á Tayabas (2nd printing 1887), is first mentioned in the Franciscan register of 1582, although Fray Diego de Oropesa arrived at this village in 1574. This is the same year given by Huerta (1862). Fray Diego belonged to the batch of pioneering Franciscans under Juan de Plasencia who were assigned to explore the area presently the provinces of Rizal, Laguna and Quezon to determine future mission sites for the Franciscans.
Gumaca was transferred to Silanga on neighboring Alabat Island in 1638 but after the Dutch reduced the town to cinders in 1665, it was decided to return the town to the Luzon mainland. Placed under the jurisdiction of the diocese of Nueva Caceres (Naga), Gumaca was officially raised to parish status in 1726. Eventually it was transferred to the diocese of Lipa in 1910, to Lucena in 1950, until it became the seat of a diocese in 1984. It assumed as titular patron San Diego de Alcala, OFM, the same titular as the Gumaca parish.
The town’s fortification apparently began in stages, beginning in the late 18th century. By the second half of the 19th century, the Franciscan curates of Gumaca had so fortified the town that when Guerra visited it in the late-19th he describes the fortification as follows: “a solid wall runs across the beach, beginning at the river which gives the town its name. Over this is a wooden bridge, which links the town to the bulwark of Santa María. Over the portal of the fortification, which opens to the road leading to Atimonan, are preserved carved in stone the imperial eagle of the house of Austria (Hapsburg), a coat of arms also displayed at the ruinous walls of the casa tribunal. A wall encloses the settlement on the seaward side with its castle of San Diego (de Alcala). The construction of this fortification demonstrates a competent hand and the solidity of its construction have maintained the fortification in good condition after so many years. On its platform is a heavy iron cannon. With these two fortifications and two others named San Sebastián and San Miguel is defined a quadrilateral. These structures are linked by a palisade of molave trunks” (Chapter 17).
The person responsible for building the connecting wall that faced the sea was Fray Francisco Costa who had the wall erected it is claimed to protect the town from the southwest monsoon. It was this same wind that brought slave-raiding vessels from the south, so Fray Francisco may also have had these marauders in mind when he raised the walls.