The Castiglioni architectural studio was started in 1936 by di Livio Castiglioni, the elder of the Castiglioni brothers. He had graduated in the same year and his father, a sculptor, had given him some rooms that he had been using in Corso di Porta Nuova 52 in Milan.
https://wannenesgroup.com/magazine/en/the-achille-castiglioni-foundation-a-house-of-ideas/