Many churches worldwide are of considerable historical, national, cultural, and architectural significance, with several included in the list of UNESCO World Heritage Sites.[7] The Greek kyriakon, 'of the Lord', was used of houses of Christian worship since c. AD 300, especially in the East, although it was less common in this sense than ekklesia or basilike.[1] In the second half of the third century AD, the first purpose-built halls for Christian worship (aula ecclesiae) began to be constructed.[8] From the 11th through the 14th centuries, a wave of cathedral building and the construction of smaller parish churches occurred across Western Europe.The Romanesque style is defined by large and bulky edifices typically composed of simple, compact, sparsely decorated geometric structures.Frequent features of the Romanesque church include circular arches, round or octagonal towers, and cushion capitals on pillars.Gothic churches lost the compact qualities of the Romanesque era, and decorations often contained symbolic and allegorical features.The first pointed arches, rib vaults, and buttresses began to appear, all possessing geometric properties that reduced the need for large, rigid walls to ensure structural stability.Many architects used these developments to push the limits of structural possibility – an inclination that resulted in the collapse of several towers whose designs had unwittingly exceeded the boundaries of soundness.[11] In the fifteenth and sixteenth centuries, the changes in ethics and society due to the Renaissance and the Reformation also influenced the building of churches.[13] The Protestant parishes preferred lateral[clarification needed] churches, in which all the visitors could be as close as possible to the pulpit and the altar.[18][19] After the Roman Empire became officially Christian, the term came by extension to refer to a large and influential church that has been given special ceremonial rights by the Pope.Cathedrals tend to display a higher level of contemporary architectural style and the work of accomplished craftsmen, and occupy a status both ecclesiastical and social that an ordinary parish church rarely has.Such churches are generally among the finest buildings locally and a source of national and regional pride,[21] and many are among the world's most renowned works of architecture.[41] Old and disused church buildings can be seen as an interesting proposition for developers as the architecture and location often provide for attractive homes[42] or city centre entertainment venues.[43] On the other hand, many newer churches have decided to host meetings in public buildings such as schools,[44] universities,[45] cinemas[46] or theatres.[note 1] In contrast, some estimates suggest that the United States has the highest number of churches in the world, with around 380,000,[60] followed by Brazil and Italy.These cities include Adelaide,[63] Ani,[64] Ayacucho,[65] Kraków,[66] Moscow,[67] Montreal,[68] Naples,[69] Ohrid,[70] Prague, Puebla, Querétaro, Rome,[71] Salzburg, and Vilnius.[82] Many churches worldwide are of considerable historical, national, cultural, and architectural significance, with several recognized as UNESCO World Heritage Sites.