Sabratha's port was established, perhaps about 500 BC, as a Phoenican trading-post that served as a coastal outlet for the products of the African hinterland.The Phoenicians gave it the Lybico-Berber name 'Sbrt'n. Sabratha became part of the short-lived Numidian   Kingdom of Massinissa before being Romanized and rebuilt in the 2nd and 3rd centuries AD. The Emperor   Septimus Severus was born nearby in Lebtis Magna, and Sabratha reached its monumental peak during the rule of the Severus. The city was badly damaged by earthquakes during the 4th century, particularly the quake of AD 365. It was rebuilt on a more modest scale by governors. Besides its magnificent late 3rd century theatre that retains its three-storey architectural backdrop 'The Roman theater at Sabratha in Libya is today one of the most impressive Roman monuments in North Africa. The Sabratha Theater is distinctive for its sculptured pulpit, which is decorated with a variety of mythological, historical, and genre scenes. A UNESCO placed the site in its "World Heritage List" The research aim to study the material building which used in the theatre such as limestone's, marbles and mortars, and effects of coastal environmental conditions which collapsing, disintegration and damage it by using analysis, investigations and materials tests such as XRD, XRF, PM, and SEM to identification of elements and minerals composition and its alteration. Physio-mechanical properties of building materials was also evaluated