Moscow has developed in circles around the original historical center. Today, Muscovites divide their city into four road rings. The first one, Bulvarnoye Koltso (Boulevard Ring), contains the very center of the city, the Kremlin, as well as the Red Square and some other tourist attractions. The second ring road draws a circle with a diameter of around five kilometers around the Kremlin and covers what is considered the city center. The area is referred to as Sadovoye koltso, the Garden Ring. The Third Transport Ring (TTK) is a high-speed freeway. The fourth ring is enclosed by the Moscow Automobile Ring Road (MKAD). The MKAD is the official city boundary, although there are huge areas outside the ring that are also officially part of the city area.