خوان الأول ملك قشتالة
The armed resistance met the Castilian army on April 6, 1384, in the Battle of Atoleiros. General Nuno Álvares Pereira won the battle for the Aviz party, but victory was not decisive. John I of Castile then retreated to Lisbon in May and besieged the capital, with an auxiliary fleet blocking the city's port in the river Tagus, in a severe drawback to the independence cause. Without the capital and its riches and commerce, little could be done to free the country from the Castilian king. On his side, John I of Castile needed Lisbon, not only for financial reasons, but also for political ones—neither he nor Beatrice had been crowned as monarchs of Portugal, and without a coronation in the capital he was only a designated king.