The building materials of the Theatre of Marcellus, reflect Roman builders' careful selections of tuff and travertine for dimension stone and volcanic aggregates for pozzolanic concretes. The vitric-lithic-crystal Tufo Lionato tuff dimension stone contains a high proportion of lava lithic fragments, which increase its compressive strength and decrease water sorption, enhancing durability. Sophisticated installations of travertine dimension stone reinforce the tuff masonry, which is integrated with durable concrete walls and barrel vaults. The pozzolanic mortars of the concretes contain harenae fossiciae mainly from the intermediate alteration facies of the mid-Pleistocene, scoriaceous Pozzolane Rosse pyroclastic flow. They have pervasive interpenetrating pozzolanic cements, including strätlingite, similar to highquality, imperial era mortars. Concrete walls are faced with refined Tufo Lionato opus reticulatum and tufelli, and opus testaceum of fired, greyish-yellow brick. The exploratory concrete masonry, which includes some of the earliest examples of brick facings and strätlingite cements in Rome, and the integration of these materials in complex architectural elements and internal spaces, reflect the highly skilled workmanship, rigorous work-site management and technical supervision of Roman builders trained in republican era methods and materials.

ABSTRACT:This paper is the first report about the development of a methodology for the virtual Anastylosis of elements belonging to an archaeological site, based on the 3d modeling of fragments. This research is the result of the cooperation between Università Roma Tre, Dipartimento di Architettura and Sovrintendenza Capitolina ai Beni Culturali; several 3D survey, modeling, information systems and archaeology experts were involved. The purpose of the research was to study the complex and stratified site of the Arch of Titus at the Circus Maximus aiming, first of all, at completing the existing traditional graphic documentation using cataloguing and survey innovative methodologies, and, secondly, at supporting new proposals for the reconstruction and Anastylosis of the Arch itself. This tested methodology whose fundamental element is the three-dimensional textured model of each fragment, can also be used in other sites and contexts.

The methodology presented in this paper, based on the 3d modeling of fragments and the use of a 3D GIS, has studied some of the procedures for the virtual reconstruction of archaeological complex sites, such as the Arch of Titus. This method is based on the factorization of the reconstruction process in a planimetric anastylosis, a following altimetric anastylosis and a three-dimensional volumetric anastylosis that brings together information derived from the first two. Our research also makes use of existing traditional graphic documentation, from which it takes its cue

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