276 CARNEGIE INSTITUTION OF WASHINGTON. 



Washington, Henry S., Washington, D. C. Report on ancient Roman 

 building materials. 



During June, July, and August, 1922, I collaborated with Professor 

 Tenney Frank, professor of Latin at Johns Hopkins University, in study- 

 ing the mortar, brick, and tuff used in the buildings of ancient Rome. The 

 investigation was undertaken following a suggestion by Miss Van Deman 

 (in Year Book No. 21) that for a number of years "an exhaustive chemical 

 and microscopic examination of the Roman bricks and mortar of the different 

 periods" has been felt to be advisable. A study of the Roman volcanic tuffs 

 was included because they form one of the earliest and most important of the 

 ancient building materials. 



Especial attention was paid by us to the ruins in the Forum Romanum 

 and on the Palatine Hill, where every ancient building was examined from 

 the point of view of its material, its known history and restorations being also 

 considered. Some specimens of construction materials of all three classes, 

 mortar, brick, and tuff, were collected from many of the buildings. Our 

 study and the collection of specimens were greatly facilitated and, indeed, ren- 

 dered possible by the interest shown in the work by, and the cooperation of, 

 Commendatore Giacomo Boni, Director of the Excavations at the Forum and 

 the Palatine, and his First Assistant, Ingegnere Torquato Ciacchi. Many 

 quarries of tuff, both ancient and modern, were visited and specimens of the 

 material were collected. The occurrence of these volcanic tuffs and their 

 uses in early Roman architecture have been a special study of Professor 

 Frank. 



The purposes of the investigation are twofold. The chief one is archae- 

 ological, and this has several special objects in view. One is the determina- 

 tion of the chemical and mineral characters of the material and the com- 

 position of the mortar, brick, and tuff, as a contribution to the study of 

 Roman architecture, for which a better knowledge of the characters of the 

 materials is desirable. Another is the classification of the three kinds of 

 material, based on the chemical, mineral, and textural characters, the classi- 

 fications being so devised that they may be usable by archaeologists without 

 such special knowledge; that is, the classifications should be, so far as possi- 

 ble, expressed in the megascopic characters. The provenance of the various 

 materials and of their components (as with mortar) should be ascertained. 

 In a given mortar, for example, we should know whether it was made with the 

 admixture of powdered brick or of pozzolana, and in the latter case whether 

 the volcanic material came from the neighborhood of Rome or of Baise. 

 The correlation between the characters of the material and the builders who 

 used it is the most important archaeological problem. Various materials 

 were commonly used at different times and, especially, the different Roman 

 emperors who were most active in building operations had their favorite 

 or usual kinds of construction material, whether tuff, mortar, or brick, which 

 are thus more or less characteristic of their work. It is possible by such 

 correlations, even in the absence of stylistic, epigraphic, or literary evidence, 

 to determine the original builder of a temple, basihca, or other construction, 

 and those who restored or altered it in later times. In this way the important 

 dates in the history of many ancient Roman buildings may be traced with 

 considerable accuracy and certainty. Dr. Van Deman, in her work at 



