In July of 1569 in Lublin an international union of a specific nature was agreed to. As a result of the union decrees the Crown of the Polish Kingdom and the Grand Duchy of Lithuania was formed with a single foreign policy and a single ruler, who was elected at a joint session of the Sejm (Parliament). The Polish-Lithuanian Union became one of the first real European supranational unions. It was one of the longest functioning precursors of the contemporary European Union. The Union lasted until the partition of Poland towards the end of the 18th century.

On the photo the castle in Lublin - the site where the Union was signed and the original of the Lublin Union Act.