The first pyramid built was the graded one of Zoser, which exists even today, in Sakkarah, the necropolis of Menphis. Built in the year 2650 BC by the architect Imhotep, initially it was supposed to be a mastaba but later floors were added until they reached six. It is the oldest monumental work in stone known to man that exists. Its exterior walls are made of white limestone. The wall has 14 doors, 13 of them false.