The Christian occupation of the square of Amposta materializes on 1148 in the campaign of Ramon Berenguer IV for the conquest of Tortosa. The castle of Amposta, with its terms, was given to the Order of the Hospital of Sant Joan de Jerusalem, who established the Priorat or Castellania d’Amposta, which from 1154 became the center of the possessions of the order within the territory of Catalonia-Aragon. The situation remained until 1280, when the Hospitallers exchanged the castle and the village in exchange for the territories of Onda and Gallur, following the border advance in the Christian military conquest of the Muslim kingdoms.
In 1282 Pere el Gran granted the town letter to Amposta. Its deltaic situation, economic difficulties and piracy prevented the development of the town well into the modern era. In the 19th century the French War and the Carlist Wars also brought him many difficulties. In the second half of the century, however, the construction of the Canal de la Dreta de l’Ebre and the colonization of the Delta for the expansion of rice cultivation marked the beginning of a process of fundamental expansion, continued to this day.
The first document mentioning a church in Amposta dates from 1097, when Ramon Berenguer III donated to the abbot of Sant Cugat a set of lands south of the Ebre that had not yet been conquered. In this document, it is called the church of the Sant Sepulcre d’Amposta.
At the end of the 13th century, coinciding with the beginning of the town, a first church would be built to serve the inhabitants of Amposta. This church should already exist in 1314, since the Bishop Paholac visited this town during his pastoral visit and already appears under the title of Santa Maria. In the 15th century, pastoral visits were repeated, without any description of their architectural characteristics.
During the siege of the castle of Amposta between 1465 and 1466, the church suffered several damages as a result of the bombings, along with other buildings of the town, such as the mill of Miralles.
This medieval church, could later be known as the Chapel of Santa Susanna. Despite the lack of documentation that allows us to affirm, the situation of the old chapel next to the river, as well as the way in which it is represented in the ancient cartography, bring us closer to the plan of a building built in medieval times.
Archaeological excavations carried out in recent years have revealed the plan of an old church and the cemetery in front of the current church of the Assumption. The building occupied most of the space, bordering to the north with the current street Nou, to the west with the street Major, to the east with the cemetery and to the south with a street today disappeared. It would be a single-nave building with an apse facing northeast and with perimeter walls of more than two meters thick made of lime mortar. It seems that it could have been fortified, responding to the security needs of the unprotected population in the face of the pyric attacks by the fall of the Castle.
In May 1776, the consistory of the City of Amposta and representatives of the Church granted the construction deed in favor of the architects and builders of Tortosa, Francesc Mulet and Andreu Moreno, for a price of 4,100 pounds, Valencian silver coin. But due to economic difficulties, the work was delayed and finally provoked a new project, to save money, in charge of the Valencian Manuel Blasco. But the problems for the payment of the works continued and the building did not progress, paralyzing definitively in 1826.
During the Second Carlist War it was used as a barracks by the royal troops, suffering considerable damage. Around 1850, thanks to a donation from Queen Isabel II, work began again and ended around 1875, although the façade was unfinished. During the Spanish Civil War, it was converted into a supply and wholesale distribution market.