A string orchestra is unerstood as an orchestra composed solely of instruments of the violin family. These instruments are the violin, the viola, the violoncello and the double bass (the last sometimes considered an anomaly because of its resemblance to the viol family.). String orchestras can be of chamber orchestra size ranging from between 12 and 21 musicians (6,5,4,4,2 = 21) sometimes performing without a conductor, or consist of the entire string section of a large symphony orchestra which could have 60 musicians (16,14,12,10,8 = 60). A twentieth century development has been the reappearance, minus continuo, of the concerto grosso pitting of soloists against the full ensemble.