2004 AD., Austria, Enlargement of the European Union commemorative, Vienna mint, 5 Euro, KM 3122.

Austria, Republic, Enlargement of the European Union commemorative, engravers: Helmut Andexlinger (obv.) and Thomas Pesendorfer (rev.), non circulating issue, Vienna mint, 2004 AD.,
5 Euro (ø 28,5 mm / 10,00 g), 0.800 silver, 10,00 g theor. mint weight, mintage 400.000 , axis medal alignment ↑↑ (0°), plain edge, nonagonal (9-sided) shape,
Obv.: REPUBLIK ÖSTERREICH / 5 / · EURO · , big value number within circle of Austrian shields, legends and denomination around.
Rev.: EU-ERWEITERUNG 2004 / € - {THS} // CESKA REPUBLIKA / EESTI-KYTUPOΣ-LATVIJA / LIETUVA-MAGYARORSZAG-MALTA / POLSKA-SLOVENIJA / SLOVENSKA REPUBLIKA , map of Europe, countries of the 2004 extension named below and marked on the map by a flag, Euro symbol in left field, engraver´s {THS}-monogram at r. edge.
KM 3122 ; Schön 304 .

Year / Mintage
2004 275,000
2004 125,000 brilliant uncirculated issue

The 2004 enlargement of the European Union was the largest single expansion of the European Union (EU), in terms of territory, number of states, and population to date; however, it was not the largest in terms of gross domestic product. It occurred on 1 May 2004.

The simultaneous accessions concerned the following countries (sometimes referred to as the "A10" countries): Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, and Slovenia. Seven of these were part of the former Eastern Bloc (of which three were from the former Soviet Union and four were and still are members of the Central European alliance Visegrád Group), one of the former Yugoslavia (together sometimes referred to as the "A8" countries), and the remaining two were Mediterranean islands and former British colonies.

Part of the same wave of enlargement was the accession of Bulgaria and Romania in 2007, who were unable to join in 2004, but, according to the Commission, constitute part of the fifth enlargement.

More on https://en.wikipedia.org/wiki/2004_enlargement_of_the_European_Union