Tanuan may have been the first fortified church complex in Leyte. In 1630, Fr. Melchor de Vera, builder of the fort at Zamboanga City, first broached the idea of fortifying the Visayan churches against marauders. De Vera set the example, which others followed.
In 1610, Tanauan on the eastern coast of Leyte was founded by the Jesuits. In 1687, according to Putong, the Jesuits suggested that a church be built in the place. A Chinese migrant from Luzon, Juanillo Siengco who had arrived in Tanauan in 1661, was employed to build a church of wood and stone.
In 1704, the present Tanauan church was completed. This is the same year noted as the foundation of the parish. In 1768, Tanauan was ceded to the Augustinians then in 1843, it was transferred to the Franciscans. But the Franciscans were not able to provide personnel until 1846, when Salustiano Bus, OFM, began to minister in Tanauan—although intermittently. It was the following year, 1847, when the Franciscans were able to assign Francisco de Paula Marquez, OFM to take permanent charge of the place.
Fray Agustin Maria de Castro, an Augustinian assigned to Leyte after the Jesuit expulsion, lists Tanauan as among the towns with stone churches built by the Jesuits. He also notes the fortification made of stone and the supplies of armament in the church complex.
When the Franciscans took charge of the place they found a solidly built church with a defensive wall surrounding it and a bulwark at every corner. Huerta (1865: 349) describes the fortification: “[the church and convento] are found surrounded by a wall of stone of uniform dimension, with a bastion at each corner, the walls were built as a defense against the Moros, although the wall is greatly deteriorated.”
Fray Marquez, who was an avid builder, lengthened the church nave, so that the church measured 228 ft. in length and 22 ft. in width. To disguise the ungainly proportions of the church he added a chapel at the gospel side, 42 by 42 ft. in dimension. In 1850, he repaired the convento and its roof. In 1860, The church may have been further repaired by the addition of a transept. A memorial marker is found on the transept wall with this date.
The church fabric as repaired by Marquez has been greatly altered by 20th-century renovations. The convento is now a school. Some fortification walls still stand behind the church. But the church has a new façade and bell tower. The interior has been repainted and the old retablos replaced by new ones. The Stations of the Cross and the image of Our Lady of the Assumption, the patroness, may be old; the statue probably dates to the 18th century.
Tanauan traces its fortification to the Jesuit Melchor de Vera who in the 17th cent broached the idea of fortifying the mission churches of the Visayas. It is uncertain what type of fortification de Vera built. Was it mortar and stone or a field-type, consisting of a palisade fortified with earth? The present fortification was in construction until 1704. It is now impossible to determine which part of the fortification is the handiwork of de Vera and which part is of a later construction. In 1884, Huerta asserts that the walls were already in disrepair. Today, very little remains of the fortification. Some walls stand behind the church apse.