Architects Without Buildings.

The Castiglionis were a Milanese family of makers before they were designers. Their father, Giannino Castiglioni, was a sculptor — the kind whose work you walk past in the Cimitero Monumentale without knowing whose hand it was. Three of his sons went to the Politecnico di Milano and came out architects. Livio, the eldest, born in 1911. Pier Giacomo, born in Monza in 1913. Achille, born in Milan in 1918.

Pier Giacomo left the Politecnico in 1937 and set up a studio with Livio the following year. Achille finished his degree in 1944, after the war interrupted it, and joined them. Livio drifted out in the early 1950s to pursue sound and lighting on his own — he is the brother most people don't name, and the one who later co-designed the Boalum, the lamp that looks like a length of drainage hose. From then on the studio was two people, and stayed two people until 1968.

How two architects design as one

The partnership is unusually hard to separate into individual authorship, and the studio never bothered trying. The Salone del Mobile's own account of Achille puts it plainly: they tackled the same problem together, arrived at the good idea together, and built the model together. Every object from those years carries both names, in that order or the reverse, with no division of labour recorded anywhere. Pier Giacomo's stated position was that design "must be simple and logical — the result of a process of reduction, elimination, and simplification." Achille's was shorter: if you are not curious, forget it.

Two addresses hold the whole story. From 1945 the studio worked out of Corso di Porta Nuova 57. In 1962, with the building slated for demolition, they moved to Piazza Castello 27 — a few hundred metres from the Sforza castle, four rooms on a courtyard. Achille worked there for the next forty years.

The received story is that the Castiglionis were designers who happened to hold architecture degrees. That's backwards. They entered the profession as architects and urban planners, competed for real commissions, and won some. The built output is small, but it isn't a footnote — and the three Milanese projects below are the ones that explain the objects.

Palazzo della Permanente, 1949–1953

The 1943 bombing of Milan gutted the city's nineteenth-century exhibition palace on Via Turati. Only the street facade — a red Verona stone front by Luca Beltrami, finished in 1886 — was left standing, and it was protected as a national monument. In 1949 Pier Giacomo and Achille, with Luigi Fratino, won the reconstruction competition against sixteen other entries. Work finished in 1953.

What they did with the site is the most architectural thing in their catalogue. The old facade stays, reopened as three separate entrances. Behind it, the compartmentalised classical galleries are replaced by flexible halls with movable wall panels, lit by cylindrical skylights cast in glass-reinforced concrete, heated through the floor. A thirteen-storey office tower, 53 metres, goes up alongside — exposed concrete beams, ceramic cladding, deliberately separated from the low horizontal exhibition volumes rather than blended into them. Preserved monument at the front, adjustable machine behind it, and no attempt to pretend the two are the same building.

Chiesa di San Gabriele Arcangelo in Mater Dei, 1956–1959

A parish church on Via Termopili, off Viale Monza, in a district of ordinary apartment blocks. The brothers described the intent as a house among houses: no dome, no campanile drama, a facade organised around one large sail-like plane and framed by two Y-shaped pillars. Inside, a single nave about 7.5 metres high under a flat roof on reinforced concrete beams, with fourteen pillars corresponding to the Stations of the Cross. Bardiglio marble with white, black Belgian and red inlays. The baptistery is set behind a geometric cross of firebrick-red glass block. Light is graded deliberately from a shadowed entrance to a bright presbytery — the same move as the skylights at the Permanente, applied to liturgy instead of paintings.

Splügen Bräu, 1960

A beer hall and hot-food counter on Corso Europa, fitted inside an office building by Luigi Caccia Dominioni. Booths in rows on three levels, stepping from ground to +2.40 metres. A long wooden counter and its run of seating doubled by a full-length mirror. The atmosphere the brothers were after was old railway carriage, which is also roughly what the room's Neo-Liberty detailing reads as. The bar is gone. Its pendant lamp — a spun aluminium shade with the ribbed profile of a piece of industrial tooling, designed for the room in 1961 — went into the Flos catalogue and is still in production sixty-five years later. That trade is the whole issue in one object.

Postwar Milan is the reason the Castiglioni catalogue looks the way it does. The city that was rebuilding itself in the late 1940s had very little public architecture to hand out and an enormous appetite for exhibiting things. Four institutions did most of the shaping.

The pavilions were the architecture

The exhibition work deserves better than the "graphics and stands" filing it usually gets. One RAI pavilion at the Fiera, designed with Enzo Mari, ran 36 by 11 metres on perimeter pillars with iron trusses and a flat roof, assembled from modular elements that worked indoors or out. The brothers then left the pavilion entirely open and hung the actual exhibition inside it from cables, in a suspended plastic element. Structure and content deliberately don't touch. It is a building-scale idea executed with a three-week lifespan.

In 1957 the brothers contributed to Colori e forme nella casa d'oggi at Villa Olmo in Como — one of the founding exhibitions of Italian design culture. They showed two seats that are still the most misread objects they made.

Sella is a racing bicycle saddle on a stainless steel column, mounted on a heavy hemispherical cast-iron base. It does not stand still; it rocks, and you balance on it. The stated use case was the telephone — a perch for a call you don't intend to settle into. Mezzadro is a stamped steel tractor seat fixed with a single wing screw to a curved steel spring, with a turned wooden crossbar as a footrest. The spring is a cantilever. The seat is a mass-produced agricultural part, unmodified, still painted its factory colour.

Neither was a provocation about art. The tractor seat is there because someone in Lombardy already stamps that shape by the thousand, it is comfortable, and buying it costs a fraction of tooling a new one. The spring is there because a cantilever gets you a seat with no back legs. Every component announces what it does and where it came from. That is an engineer's argument dressed as a joke, and the market took a long time to get it — Zanotta didn't put Mezzadro into production until 1971, and Sella waited until 1983.

Toio, 1962

The same logic, pointed at light. Toio is a 300-watt car headlamp — imported from the United States, and therefore 125 volts in a 220-volt country. So the transformer sits at the base as the counterweight, unhidden, doing two jobs. The stem is nickel-plated brass, hexagonal, telescopic. The cable runs up the outside through fishing-rod rings, because fishing-rod rings are a solved problem for guiding a line along a pole and cost nothing. Nothing is concealed and nothing is decorative. It is in the collection of MoMA.

Flos was founded in 1962 in Merano, by Cesare Cassina and Dino Gavina with Arturo Eisenkeil, initially around an imported American polymer sprayed over wire frames — the "cocoon" technique. The Castiglionis were there from the start, and 1962 is the year the studio produced the two lamps everyone can picture.

Arco starts from a domestic complaint. You want light directly over a dining table; the fixture has to hang from the ceiling; drilling and wiring a ceiling in a rented Milanese flat is not a thing you do. So: put the light source two metres away from its own base and cantilever it there. The arc is telescoping stainless steel with a reach of roughly 2.2 metres, ending in a polished aluminium shade. The base is a block of white Carrara marble weighing around 65 kilos, which is what it takes to hold that moment. The lineage is a street lamp, and the brothers didn't hide it.

Then the detail that gives the object away as architects' work: the marble base has a hole drilled through it, sized for a broomstick, so two people can thread a pole through and carry the thing. A designer solves the lamp. Someone who has thought about a construction site solves getting the lamp up the stairs.

What else came out of the studio

Pier Giacomo died in Milan on 27 November 1968, at fifty-five. He had been teaching at the Politecnico di Milano since 1964. Achille took a professorship at the Politecnico di Torino in 1969, held it until 1980, then taught industrial design in Milan until 1993 — several thousand students across the two schools.

The teaching is where the method was written down, and it is stubbornly unglamorous. Start from the function. Reduce, eliminate, simplify. Look at what already exists and at how people actually behave around objects, and prefer the component someone else already manufactures well. Achille collected what he called anonymous design — unsigned everyday things, a bottle opener, a spring clip, a tool with an obviously correct handle — and used them as teaching material. The four rooms at Piazza Castello are still full of them.

The recognition arrived late and thoroughly: honorary degrees from the Royal College of Art and the Politecnico di Milano, nine Compasso d'Oro awards, permanent collection status at MoMA and the V&A. In 1997 MoMA gave him a retrospective, Achille Castiglioni: Design!, curated by Paola Antonelli. He died in December 2002.

Achille kept working at Piazza Castello 27 for thirty-four years after his brother's death, and the room was never cleared. In January 2006 his heirs signed a five-year agreement with the Triennale di Milano to open it as the Studio Museo Achille Castiglioni. The Fondazione Achille Castiglioni was established on 14 December 2011 to catalogue and digitise the whole contents — drawings, models, prototypes, films, photographs, conference recordings, the object collection, sixty years of it. Two of Achille's former assistants of more than twenty years, Antonella Gornati and Dianella Gobbato, run the archive work on the premises.

It is open to the public by guided tour, in small groups, on weekday mornings. You get four rooms, the drawing boards, the prototypes that didn't ship, and the anonymous objects. In 2014 Milan named a street after all three brothers — Via Fratelli Castiglioni.