The boundaries between the differen parts of Moscow are defiend by the river, and the walls that once surrounded the city. The Kremelin border is shown in blue, which is an impassible wall. To the south it is situated nex to the river. The red edge indicates the medieval wall. It is now a boulevard with greenspaces. The area in the red edge is the oldest part of the city, with mostly low-rise historical residential or government buildings. Most of the old churches are also located in this area. The edge is the line defining where more modern Moscow begins, which has much of the business. Beyond the green line is the surburban area of Moscow, which stretches on for several more miles before it gently dissolves into countryside.