Mantralaya is the administrative headquarters of the state government of Maharashtra in South Mumbai, built in 1955.
Mantralaya was earlier known as Sachivalaya. (Sachiv- Secretary, Alaya- House, meaning Secretariat). Most of the head quarters of state govts in India are known as Secretariats. However, since Ministers (Mantri in Marathi/Hindi) also sit in the same building and to underline the fact that Ministers are ultimate bosses in democracy, the name was changed to Mantralaya in the early eighties.
Mantralaya is a Six storeyed building with most of the departments of state government in this building. The Chief Minister and Deputy Chief Minister sit on the sixth floor. The Chief Secretary, i.e. topmost bureaucrat, sits on the fifth floor. Due to increasing number of departments and the staff, the new "annexe" building was built later on. Further, a new administrative building of 13 floors was constructed later on, opposite Mantralaya to accommodate additional departments.