What Gaudí Couldn't Build

In a stone workshop on the edge of Barcelona in 2026, structural engineer Tristram Carfrae watched a team of builders set the final piece of the Sagrada Família's central spire into place, more than 140 years after Antoni Gaudí first modeled it. The Tower of Jesus Christ is now the tallest tower on the Sagrada Família — and at 172.5 metres, among the tallest structures in the city.

Gaudí designed the tower in the 1880s, using hanging plaster chains, ruled surfaces, and physical models that he trusted more than drawings. The form he produced was not, at the time, buildable. Steel fabrication in Spain was limited, wind engineering on slender masonry was guesswork, and the construction techniques needed to translate a hanging-chain model into a vertical stone-and-concrete spire did not exist. So the tower waited. Stonemasons, sculptors, and a rotating cast of architects and engineers worked on everything else around it, year after year, while the central spire stayed on paper.

Carfrae, a structural engineer and designer at Arup, was tasked over a decade ago with making Gaudí's "unbuildable" design buildable, according to BBC Inside Science, which features him as the primary actor on the engineering side of the project. The episode frames his work as finishing a problem Gaudí could not have finished in his own lifetime, using tools Gaudí could not have imagined. The work involved modern wind-tunnel testing, finite-element analysis, prefabricated stone panels, and a careful reading of the physical models Gaudí left behind to recover geometric decisions that the architect never wrote down.

What changed was not Gaudí's vision. The geometry, the proportions, the ruled surfaces, and the symbolic intent of the spire were preserved. What changed was the engineering culture around the project. The original construction relied on rule-of-thumb masonry and intuition. Carfrae's team, and the succession of structural engineers before them, treated the spire as a problem in computational analysis: how to keep a slender stone tower stable in Barcelona's wind regime, how to manage thermal expansion in a structure that would see hot summers and cool Mediterranean winters, and how to assemble the panels in a way that did not require scaffolding to grow with the building.

That last problem is the one most readers will not see. The Sagrada Família has been under construction since 1882, and the team finishing the central spire in 2026 includes people whose predecessors started work before the architect died. Different generations of builders, model-makers, and stonemasons have each worked from different drawings, sometimes with conflicting assumptions about geometry, load paths, and material behavior. The completion of the central spire is, among other things, an act of reconciliation: bringing the geometry of the 19th century into agreement with the engineering of the 21st, in a single building that has absorbed both.

The central spire reached structural completion in February 2026, with an inauguration scheduled for June 2026. The tower is finished; the church is not. Full completion of the Sagrada Família — including the Glory Façade and interior stairway — is not expected until 2034. The structural milestone is real; the project as a whole is still open.

The forward question is whether the Sagrada Família is the last of its kind, or a template. Architectural offices now design forms that their own firms cannot yet build. Complex curved facades, mass-timber shells, and freeform concrete structures increasingly rely on computational design tools that contractors have to translate back into something a builder can assemble on site. The Sagrada Família suggests one model: a long institutional memory, a structural engineer willing to commit a career to one problem, and a client patient enough to wait. In most contemporary projects, none of those conditions hold.

It also suggests a less comfortable reading. A 144-year construction timeline is not a triumph of vision alone. It is also the product of a city that absorbed the cost, a labor force that accepted the discontinuity, and a public that tolerated the slow, visible presence of an unfinished cathedral in its skyline. Carfrae's engineering is real. The tower of Jesus Christ is now in place. But the conditions that made the project possible are not easily reproduced, and it is worth asking which of them, exactly, the profession is supposed to learn from.

For now, the tower stands. Whether it is the closing chapter of a 19th-century problem or the opening argument for a new class of unbuildable designs depends on how the next generation of structural engineers chooses to spend the next 140 years.