Romania was once also the cradle of Yiddish theatre, and to this day Bucharest is home to a State Jewish Theater, despite the small number of Jews remaining in the country. In the technical domain one can note the achievements in the field of aviation made by Traian Vuia, Aurel Vlaicu, Aurel Persu, and Henri Coandă and also the works of George Constantinescu in the fields of engineering and sonics. Also many achievements have been made in the architectural and engineering domain, thus Bucharest became known as "the small Paris". The longest bridge in Europe was constructed by Anghel Saligny linking Dobruja with the rest of Romania, the Peleş Castle became one of the most beautiful and modern castles in Europe. Folk music is the oldest form of Romanian musical creation, characterized by great vitality; it is the defining source of the cultured musical creation, both religious and lay. Conservation of Romanian folk music has been aided by a large and enduring audience, and by numerous performers who helped propagate and further develop the folk sound. Two of them, Vasile Pandelescu, and Dumnitru Zamfira are one of the most famous examples of Romanian folk musicians. Before the major incorporation of more modern instruments that found their way into Romanian folk music, older instruments such as the Tobă (double-headed drum, also known as the Tabul or Davul), Surlă (also known as the Zurna in other parts of the Balkans), Caval (ancient shepherd's pipe), Cobza (an ancient instrument related to the Arabic Oud), Vioară (violin), Cimpoi (Balkan bagpipe), and the Tamburină (tambourine, more commonly used during the times under Phanariote and Ottoman influence), were also commonly used in folk music before the introduction on some slightly more modern elements such as the widely used accordion, and clarinet. Folk music, often is accentuated with clapping, yells of tongue rolling, shouts, and whistles. The religious musical creation, born under the influence of Byzantine music adjusted to the intonations of the local folk music, saw a period of glory between the 15th-17th centuries, when reputed schools of liturgical music developed within Romanian monasteries. Russian and Western influences brought about the introduction of polyphony in religious music in the 18th century, a genre developed by a series of Romanian composers in the 19th and 20th centuries.