The history of Santa Eulària des Riu is rooted in antiquity, but the town began to develop as a formal settlement after the Catalan conquest of Ibiza in 1235. During the Islamic period, this territory was known as the Xarc district, a region rich in fertile land. The actual core of the future town was the fortified religious complex on Puig de Missa hill. The first church was founded here immediately after the Reconquista, but the current appearance of the fortress-church took shape in the 16th century, when there was an urgent need to protect the population from frequent pirate raids.
The town's development was determined by a unique combination of geographical and strategic advantages. Geography and water resources played a key role: the town emerged at the mouth of the only river in the Balearic Islands. Constant access to fresh water was a decisive factor for life and farming in the archipelago's arid climate. Furthermore, the elevation of Puig de Missa allowed for control over the surrounding area and served as a reliable refuge for valley residents during enemy attacks, encouraging the concentration of the population around the hill.
The economy of early Santa Eulària was built around agriculture and grain processing. Thanks to the energy of the river's flow, a system of water mills was built here, making the town the main flour milling center of Ibiza. Proximity to the sea and the presence of the river also created conditions for the development of local trade. Cultural life was closely linked to the church parish, which performed not only spiritual but also administrative functions, uniting scattered farmsteads into a single community.