The Spanish attack to Portugal started on the early morning of the 20 May, and focused on the Portuguese border region that included the main Garrison Town and Fortifications of Elvas and the smaller fortified towns of Campo Maior, Olivença and Juromenha. The main force of the Spanish Army advanced to Elvas, while two divisions advanced to Campo Maior and another division advanced to Olivença and Juromenha.
Without having their fortifications complete and defended only by a few hundred soldiers, most of them militias, Olivença and nearby Juromenha quickly surrendered to the Spanish forces.