Roma Vecchia-
  Porta Maggiore

Peperino stone

The main elements of the construction are solid stones, primarily of peperino, laid without mortar(!!)
The inner dimensions of the Aqua Claudia (the lower channel) were 1.2 m wide and 1.9 m high.
On top the lower half of the channel of the Aqua Anio Novus that was made of cement faced with bricks. Inner dimensions were 1.15 m wide and 1.25 m high. Both channels were lined with special hydraulic cement called opus signinum.