By perfecting concrete, a plentiful and cheap building material, the Romans were able to build structures quickly and without the need for vast teams of skilled craftsmen. Timber frames, or moulds, were used to provide a framework for the concrete walls; constructing them was a task that could be done by a relatively unskilled labourer. The frameworks could also be re-used, making the whole process relatively cheap, quick and efficient. This could prove vital in times of war when defensive structures needed to be built quickly.
