A common characteristic of the Minoan architecture were flat roofs. The rooms of villas didn't have windows to the streets, the light arriving from courtyards. In the 2nd millennium BC, the villas had one or two floors, and the palaces even three. One of the most notable Minoan contributions to architecture is their inverted column, wider at the top than the base (unlike most Greek columns, which are wider at the bottom to give an impression of height). The columns were made of wood (not stone) and were generally painted red. Mounted on a simple stone base, they were topped with a pillow-like, round capital.