The Allianz One tower was originally considered to be the first bureaucratic tower in La Défense. With the help of interior design agency Enfi Design, Jean Willerval worked on creating absolute flexibility. He used a square grid, both parallel and perpendicular to the partitions, and eliminated blind spaces.

On the outside, the building resembles a succession of crystalline prisms whose triangular planes oscillate with undulations, slits, and notches. These “flaws” bring light into the interior and multiply the image reflected on the exterior.

The Allianz One tower underwent a sustainable renovation project until 2015. Built 30 years ago, it has retained its crystalline appearance but has been clad in dark blue-gray semi-reflective surfaces that give it a more contemporary look.

This renovation work was carried out by the architectural firm Bridot Willerval for Allianz. Allianz One has obtained four benchmark certifications recognizing the commitment and efforts made during the renovation of the Athena Tower:

• The French HQE “Exceptional” certificate for its environmental qualities, based on fourteen criteria divided into four performance areas: eco-construction, eco-management, comfort, and health;
• The British BREEAM “Excellent” certificate;
• The American LEED “Gold” certificate for renovation;
• The BBC Effinergie Rénovation label.

The tower welcomed its first users, Allianz Group employees, in early January 2016.

Jean Willerval (1924–1996) began his career in 1959, mainly in Nord-Pas-de-Calais, his native region. His first notable works include the Saint-Jean-Bosco church in Mons-en-Baroeul and the courthouse in Lille. In 1971, the brutalism of the Masséna barracks in the 13th arrondissement of Paris, contrasting with the Nordic modernism of his early works, placed him among the proponents of an international alternative.

In La Défense, Jean Willerval began with a project that ranked first in the consultation for Tête Défense in 1980 but was never realized. In 1984, he returned to the prisms of the 1920s for the Allianz One tower. That same year, he co-designed the Descartes tower with Fernando Urquijo and Giorgio Macola. In association with Bernard Lamy, he took charge of the Gan Eurocourtage tower. After a long interruption, this project was taken over by his son, Bruno Willerval.