Today in the Middle Ages: May 9, 1386

On May 9, 1386, England and Portugal signed the Treaty of Windsor, a pledge of mutual assistance which remains in effect to this day.

The following year, the alliance was strengthened when Phillipa, daughter of John of Gaunt, Duke of Lancaster, married João I of Portugal. Their son was Prince Henry the Navigator, who inaugurated Portugal's Age of Exploration.

The two countries traded extensively, Portugal exporting wine and importing English cloth and fish.