Mandarin was the common spoken language of administration of the Chinese empire during the Ming and Qing dynasties. It arose as a practical measure, to circumvent the mutual unintelligibility of the varieties of Chinese spoken in different parts of China. Knowledge of this language was thus essential for an official career, but it was never formally defined. The language was based on northern dialects, initially those spoken around Nanjing but later switching to Beijing, and developed into Standard Chinese in the 20th century.