One of six paintings of subjects from Polish history commissioned for the Knights’ Hall at the Royal Castle in Warsaw. In the catalogues of the Stanisław August collection the painting is unnumbered; in the 1795 catalogue it is listed as: “L’Union de la Lithuanie a la Pologne par Sigismond Auguste". A real union between Poland and the Grand Duchy of Lithuania was sworn in Lublin during the reign of King Zygmunt II August on 1 July 1569. It established the Commonwealth of Two Nations and replaced the personal union introduced in the 15th century. From 1569 until 1791 Poland and Lithuanian shared not only one monarch, but also the parliament (Sejm) and had a common foreign policy, while the central authorities, treasuries and armies remained separate. The frame is decorated with a plaque inscribed: LITUANIA JUNCTA POLONIAE A. MDLXIX.