The Atomium is a 102 meter structure on the Heysel Plateau in Laeken, Brussels, built as the centerpiece of Expo 58. Engineer André Waterkeyn and architects André and Jean Polak modeled it on a single unit cell of an alpha iron crystal, a body-centered cubic lattice with nine atoms, magnified 165 billion times. Foundations went in during March 1956 and the structure was finished less than a month before the fair opened on April 17, 1958, with 20 connecting tubes holding escalators up to 35 meters long and a Schlieren lift that carried 22 people to the top in 23 seconds. Wind tunnel tests showed that the original design, balanced on its bottom sphere alone, would overturn in an 80 km/h wind, so bipods were added under the three lower spheres.

Meant to last six months, it was never taken down, and by the 2000s decades of neglect had left it badly deteriorated. A 26 million euro renovation from 2004 to 2006 swapped the aluminium skin for stainless steel, making the iron crystal more chemically accurate than it was in 1958. The stranger fight was legal. Sabam, the Belgian copyright collection society, claimed worldwide rights over images of the building, forced a US website to remove its photos in 2003, and drew a protest in 2008 when organizers in Mechelen had the Atomium erased from public snapshots. Belgium passed freedom of panorama into law in June 2016.

• Why the name joins “atom” and “aluminium” even though the shape represents iron
• The three upper outer spheres, closed to the public because nothing supports them from below
• Old aluminium cladding cut into two meter triangles and sold as souvenirs for 1,000 euros each
• The website that replaced every Atomium photo with a warning that the copyright society would sue
• A children’s sphere where school groups aged 6 to 12 can spend the night inside the monument