Gaudí and Matamala sculptors’ team were choosing casual passers-by to use them as a models for the different sculptures. They took a picture with a set of mirrors of the chosen person. In that way, they got in the same picture every part of that person and so they made the corresponding sculpture.
The chosen person to represent the Roman soldier was one of the Sagrada Família workers. Everyone was astonishes when they took the picture and realised he had six toes in each foot. Matamala proposed to sculpt only five, but Gaudí said “No” and asked to represent him just as he was, in order to show how different was someone capable to kill innocent under two years old children, even if the soldiers followed king Herod’s orders. So here we have the Roman six toes soldier.
If you want to know the Sagrada Familia, I suggest you the the Gaudí Tour.