Work has begun to complete six immense towers that officials say will make it Europe’s tallest religious building.

Designed by legendary Spanish architect Antoni Gaudí (above left) in 1883, La Sagrada Família basilica remains unfinished to this day, despite being an emblem of the Barcelona cityscape and a major attraction for tourists worldwide. Largely regarded as a modernist masterpiece, this church is one of Gaudí’s most ambitious designs, and he devoted his final years to the project. By the time of his death in 1926, it was less than a quarter complete.

Now, more than a century since the first foundation stone was laid, La Sagrada Família has entered its final stage of construction. Scheduled for completion in 2026 to coincide with the 100th anniversary of Gaudi’s death, it will be the world’s tallest church, standing 565 feet above the Catalan capital.

During a press conference on Wednesday, chief architect Jordi Fauli said that although the structure is on track to be finished by 2026, elements of decoration could take until 2030 or 2032 to complete. Once fully-built, the cathedral will feature 18 towers dedicated to various religious figures, including the Virgin Mary and the four evangelists—their varying heights designed to reflect hierarchy. The tallest of the six spires, the Tower of Jesus Christ, will rise directly from a chamber designed to support its weight and funnel sunlight into the church.

Sagrada Família has long been a point of controversy among the city’s citizens over both Gaudí’s original design and the possibility that those who continued work on it after his death disregarded it. Praised for its technical perfection by Bauhaus founder Walter Gropius and described it as “spirit symbolized in stone” by Louis Sullivan, the church was also famously called a “tactile erogenous zone” by Salvador Dali. In 2010, it became the subject of dispute when the Spanish government unveiled plans for a high-speed rail tunnel only 13 feet away.

A 3D animation of the Gaudi’s completed masterpiece: