Gelsenkirchen’s Musiktheater im Revier opened on 15 December 1959. The architect was Werner Ruhnau, who designed a complex comprising two stages for music theatre and dance. Instead of a percent-for-art scheme, Ruhnau chose to involve artists in the project right from the start so that their works of art would be on an equal footing with the architecture. He had first caught sight of Yves Klein’s monochrome paintings at an exhibition of the German sculptor Norbert Kricke at Iris Clert’s gallery in Paris in March 1957. Ruhnau was so taken with these that he called on the painter the very next day. The friendship that grew out of that first encounter would culminate in Klein having a hand in the design of the theatre in Gelsenkirchen. Klein’s connections with Germany intensified when his Monochromes featured in the inaugural exhibition of the Galerie Schmela in Düsseldorf. It was there that he met his future wife Rotraut, sister of the ZERO artist Günther Uecker. Klein submitted his bid for the artistic design of the foyer of the Musiktheater im Revier on the day of the opening at Schmela, 31 May 1957, and was awarded the contract – thanks in part to the support of both Kricke and Ruhnau – in January 1958. Just over a year later, on 22 May 1959, Jean Tinguely was likewise enlisted to create two moving reliefs for the complex. These were to be ready by August, it was stipulated. Klein had long been in Gelsenkirchen by then and was working round the clock on a blue sponge sculpture in the theatre foyer. The exhibition Collaboration Internationale entre artistes et architectes dans la réalisation du nouvel Opéra de Gelsenkirchen opened at Iris Clert’s gallery in Paris in late May 1959 – a few months before the theatre itself.