Sommaruga designed the palazzo for the Castiglioni family between 1901 and 1903, completing the work in 1904. The commission carried weight: the family wanted a residence that argued for Milan’s entry into the European Liberty conversation, and Sommaruga delivered a facade in which sculpted figures, scroll-work, and floral relief read as a single sustained gesture — the very thing the Milanese Liberty school would be measured against for the next twenty years.

The Castiglioni interior, mostly closed to the public, retains its original stucco programme and the staircase that Sommaruga conceived as a sculpted volume rather than a circulation device. The building survived the bombing of August 1943, the post-war reconstruction wave, and the speculative pressure that erased much of bourgeois Milan in the 1960s.

Today the palazzo functions as a private residence with offices on the lower floors. The exterior is freely visible from Corso Venezia; the interior can sometimes be visited during FAI open days. For a Liberty walking tour of central Milan, the Castiglioni anchors the segment between Porta Venezia and the Giardini Indro Montanelli.