As the title suggests it is unclear (to me at least) whether this particular foundation structure at the Etruscan-Roman site of Veio was either Roman or Etruscan. Certainly it is very old and of that earliest period of Roman influence. Large volcanic porous stone blocks of Tuff (or Tufa) are used and there is no evidence of any kind of mortar or cement.
This was probably the foundation for a structure such as a temple which would have been largely made of wood.
Read more about Roman wall construction and building foundations.