The engineering work for Sagrada Familia was insanely clever. Gaudi build a scale model including accurate weights for the building materials, upside-down, out of strings and weights. That way he could design non-vertical pillars that branch like trees and where all the stresses were carried by compression through the stonework. It is really a marvel of pre-computer technical design!
[1] https://memetician.livejournal.com/201202.html
[2] https://criticalista.com/2012/08/16/gaudis-hanging-chain-mod...