THE year was 1976, and, at a glance on a moonlit night, it might have appeared that Martians had landed on Pearl's Hill in a cylindrical spaceship. Only, this one is 38 storeys high. And it contains a veritable hive of interlocking split-level spaces, approaching the complexity of a Borg cube (of Star Trek extraction).

Meanwhile, another enigmatic cube had also appeared. The Rubik's Cube, which challenges players to restore 54 scrambled coloured squares on its external surface to their original six, same-coloured sides, was invented by Hungarian interior design lecturer Erno Rubik in 1974.

The two - the Rubik's Cube and the Pearl Bank Apartments (PBA), completed in 1976 and designed by pioneering post-Independence Singapore architect Tan Cheng Siong - share more than their 1970s genesis.

Their designs exemplified an approach that can be termed minimalistic rationalism.

This approach is minimalistic in that it eschews superfluous, contrived embellishment. Its aesthetic is structural, arising from the direct expression of the primary function of the object or building. And the forms gravitate towards the platonic - the cube and cylinder, in this case.

It is rationalist insofar as the forms are logically derived from the function of the object or building. Carried to consummation, nothing could be added or subtracted from such a design to serve its purpose better.

Take the Rubik's Cube. Rubik's genius lay in the design of the complex internal mechanism that enabled the squares on the surface of the Cube to be manipulated three-dimensionally. It was a cylindrical design inspired by rounded river pebbles, and fabricated to exact tolerances and with just the right balance between tightness and looseness. Externally, too, there is nothing superfluous - just simple, solid-coloured squares that serve to code the sides of the elemental cubical form.

Like Rubik's response, the hollowed cylinder of the PBA is bold, elegantly platonic, and thus deceptively simple, since the internal configuration is anything but that.

In an interview for City Lights, a documentary on Singapore architecture now available on DVD, architect Tan attributes his design to "a stroke of luck". However, it cannot be by mere chance that every interlocking interior volume, cantilevering stair and strip window that constitutes the mesmerising facade falls in place perfectly to form such a pristinely platonic 3-D jigsaw.

The puzzle on Pearl's Hill was to fit the maximum number of apartments on the small triangular hilltop site of 7,900sq m - it was the Government's first land sales site launched exclusively for residential development in 1969. At the same time, it was to deliver on the developer's promise of luxury living on a middle-income budget.

As a result, the PBA houses the largest number of apartments contained in a single block in Singapore - 272, plus eight penthouses. But belying its programmatic complexity, the layout is consummately clear.

The western-facing segment of the cylindrical building was opened to allow air and light into the hollow core. Access corridors, stairs and services line the (shorter) inner facade of this core. On the sweeping external facade, unimpeded views of the city and harbour grace the private spaces.
It is by section that the catacomb complexity is best observed. Of the 272 apartments, 248 are of the 177sq m, three-bedroom type, with spaces spread over three levels. An architect who lived in one such unit for a few years confided that he could not figure out which neighbours he shared party walls and floors with.

Though under-utilised, the PBA's communal recreation deck occupying the entire 27th level is an early precursor of the "sky lobbies" of other housing developments, including such recent projects as the upmarket BLVD and public housing at The Pinnacle@Duxton.

As an urban landmark, the PBA stands as a monumental icon of teeming density that exudes a sculptural, almost other-worldly presence.

Indeed, there is nothing in all the world quite like it - a uniquely Singaporean design. Yet its allure to buyers in the 1970s was decidedly down to earth: At around US$28,000 (about S$84,000 in the 1970s) for most of the three-bedroom units, many 1970s middle-class upgraders found the PBA to be their passage to jump orbit from the public to the private housing realm.

This story was first published in The Straits Times' Life! section on Sept 2, 2006 as part of the Urban Scrawl series which looked at seminal buildings in Singapore's landscape.