The fourth coin of the series depicts a medal presenting the last king of the Piast dynasty – Casimir the Great who earned his nickname with his great merits related to rebuilding monarchy in Poland.

"Treasures of King Stanisław August" – replicates the famous 18th century medallic series with the images of the kings of Poland, which was struck on the order of Stanisław August Poniatowski. The royal medals, designed by two outstanding medalists: Jan Filip Holzhaeusser and Jan Jakub Reichel, were struck at the Warsaw mint in the years 1791–1797/1798. The coins issued by Narodowy Bank Polski are faithful replicas of the medals, preserving the diameter and height of relief of the originals.

When Casimir the Great came to the throne, the economy of Poland was ruined, and the kingdom was depopulated and exhausted by war. Upon his death, Casimir left a kingdom which had doubled in size, was prosperous, wealthy and held great prospects for the future. He built the first Polish university, modernized economy, unified the law and introduced tax and military reforms. He also made his contribution to the Polish coinage history – he launched new monetary units, including a Cracovian grosz.

The reverse of a coin is a faithful replica of a medal with an image of a bust of king Casimir the Great, based on a portrait painted between 1768 and 1771 by Marcello Bacciarelli for the Marble Room at the Royal Castle in Warsaw. In the upper part of the coin, along the rim – an inscription in Latin: CASIMIRUS MAGNUS.

In the central part obverse – a replica of the medal obverse with a short biography of King Casimir the Great in Latin as follows: Son of Elbow-High, the first who collected all lex patriae and announced them in Wislica, fortified many towns, joined Red Ruthenia to the monarchy, had wished to make citizens and farmers contented and he fulfilled his wish; the last of the Piast dynasty. He died in 1370, after 33 years of ruling Poland, at the age of 60, on 5th November. Along the rim – inscriptions: RZECZPOSPOLITA POLSKA (Republic of Poland), 50 ZŁ (the face value). At the bottom – the year of issue (2014) and a miniature emblem of the Republic of Poland (white eagle wearing a crown).