Probably everyone has heard of the word opus? Translated from Latin the term means 'work'. This word is always used when talking about a specific way of masonry work. Following it there always stands a second term that specifies and describes the type of work. For example: when you say that the construction of the aqueduct is opus mixtum it means that mixed masonry technique is used – by using mixture of different materials or by using together two or three types of masonry. This is the most wide spreaded Roman masonry in Bulgaria.

The most commonly used building materials are stone blocks – carefully cut. In the classical Roman models they are placed next to each other with a very small gap between them. In this way the wall is smooth and precisely shaped.

A popular building material is also the Roman brick. Unlike the modern brick, it is square in shape and not very high. These dimensions gave the opportunity to use bricks also for cladding.

The Roman concrete is a significant discovery, which allowed the construction of grand buildings and structures. It is mainly used in the construction of domes and fortification walls.