The lateral naves used to be demolished to better protect the building.; stones and wooden beams were used for building entrenched storeys under the chorus or below the entire assembly of religious establishments, on consoles or flying buttresses, under abutments. The end of the 15th century stands for the last important stage in the history of fortress-church construction: in some places, after the old religious buidings belonging to the entrenched churches had been pulled down, new unitary churches were raised, made up of a single body of buildings, with entrenched storeys, supported on consoles and flying buttresses between abutments; these fortresses used to have catapults and battlements. A bell tower, built separately, was included in the precinct wall. After an age of unrest, Transylvania underwent a peaceful period and, under Louis the Great (1342 - 1382), the German colonies reached a fine economic boom. Architecture flourished rapidly and there began the construction of the large churches of towns like Sebes, Cluj - Napoca, Sibiu, Sighisoara, Medias and Brasov. Soon afterwrds, the Turks trod Europe's land for the first time and, as a result of a heavy Turkish invasion in 1491, all over the place, the defence constructions began and continued to extend systematically. Bearing the print above all of the mediaeval fortresses, the art of stronghold building - as far as towns are concerned - was then transferred to fortress churches: the walls were raised, with an open sentry road and reinforced by a row of entrenched towers. The gate was reinforced on the outside with supplementary entrenchments. Often a second or third precinct was built. The oldest fortress churches dating from those ages can be found in Tara Birsei region. The churches built in plains were reinforced as they used to be protected only up to the west tower. The most important entrenched church in Transylvania is the Prejmer one. This cross-shaped building , dating from the early Gothic, was influenced by the Kerz Cistercian construction site; it was surrounded by 12 metre high walls. These walls have a square round angle layout and are protected by stockades, water ditches, four towers and two advanced reinforcements. Within this area, the constructions supported by the precinct wall had three or four storeys; divided into 60 compartments, they had basements and 260 store houses. The fortresses are very different in the other colonised regions where the natural features of the hilly landscape have been rightly used. One of the largest and most renowned fortress-churches is the Biertan one, standing on a hill, in the centre of the village. The hall church, with three naves, dating from the late Gothic, was raised between 1500 and 1516, the preexistent chorus of the edifice having an entrenched storey. The precinct wall, dating from the same time, was reinforced during the 16th century with 8 towers; it is coil shaped, like a three tower belt, around the hill. Beside their relevance as regards the study of fortified buildings, all churches bear witness for the history of art and architecture in central Europe and mediaeval Transylvania, marked by influences from the south of Germany, Bohemia and Austria , from the Roman age to late Gothic. The entrenched churches and fortress-churches are the most relevant Saxon legacy and the token of their fusion with their own past. To point out the significance of the Saxon fortress-churches of Transylvania, a German- Romanian team revealed the project to include on the UNESCO world heritagelist some representative examples of different kinds of communities, once German, including the villages: Cilnic, Valea Viilor, Saschiz, Viscri and Prejmer (as at present onlu the Biertan fortress- church is on the list).