). Rubble or small undressed stones used
with mortar to form the concrete walls of Roman buildings. Vitruvius notes two kinds (ii. 8),
the opus reticulatum
, the more handsome but less durable kind of work;
and the primitive opus incertum
, less sightly but extremely strong,
because of the way the stones were massed together.
Concrete was extensively used at Baiae in the Augustan Age, as a foundation for edifices
built out into the sea (Tibull. 2, 3, 45; Hor.
Carm. iii. 1.33
Romans having discovered that pozzolana and lime formed an hydraulic cement (Vitruvius, ii. 6,
The most massive relic of Roman times in Great Britain, the great military wall which
extended from the mouth of the Tyne to that of the Solway, is a structure of faced concrete,
formed by erecting two faces of large stones and filling up the intervening
space with alternate courses of rubble one foot deep, and mortar four inches deep.
Many of the great Roman achievements in building, especially in distant provinces, are to be
attributed to this method of construction, which enabled them to raise, with comparatively
unskilled hands, and from materials which are accessible in most regions or easily procured,
structures which in a short time were united into solid homogeneous masses of great tenacity.
See Middleton, Ancient Rome in 1885;
id. Remains of Ancient
; and the article Domus