Poczta Polska issued a commemorative stamp on 10 September 2026 marking the 500th anniversary of Mazovia’s incorporation into the Kingdom of Poland. Prepared with the Marshal’s Office of the Mazovian Voivodeship, the design uses a historical map of Mazovia and imagery derived from medieval documents and seals associated with the region’s Piast rulers.

The sheet contains six stamps in a 3-by-2 arrangement. Its design centres on the heraldic seal of the Mazovian dukes Stanisław I and Janusz III, whose deaths preceded Mazovia’s incorporation into the Crown in 1526. Enlarged seal fragments and a palette of red, brown, gold and parchment tones extend the historical-document treatment into the sheet margins and supporting products.

The stamp measures 31.25 by 43 mm, is printed by offset on fluorescent paper, and has a stated print run of 96,000. The FDC and commemorative postmark also use imagery from the ducal seal.