Himachal Day is celebrated on April 15 to mark the formation of Himachal Pradesh in 1948, when around 28–30 princely states were merged into a single administrative unit. It began as a Chief Commissioner's Province in 1948 and became a Union Territory in 1950. Himachal Pradesh attained full statehood on January 25, 1971, becoming the 18th state of India. Its capital, Shimla, once served as the summer capital of British India.