High Quality Content by WIKIPEDIA articles! High Quality Content by WIKIPEDIA articles! A Tower block, Apartment tower, or Apartment block, Block of flats, is a multi-unit high-rise Apartment building. In some areas they may be referred to as "MDU" standing for "Multi Dwelling Unit". Apartment blocks have technical and economic advantages in areas with high population density. They have become a distinguished form of housing accommodation in virtually all densely populated urban areas around the world. In contrast with low-rise and single-family houses, apartment blocks accommodate more inhabitants per unit of area of land they occupy and also decrease the cost of municipal infrastructure.Insulae (singular insula) were large apartment buildings where the Plebs (lower class) and Equates (middle class) of Romans dwelled. The floor at ground level was used for tabernae, shops and businesses; higher floors were given to living space. These buildings were usually six or seven stories high; some were built as high as nine stories before height restrictions came into effect.