A gated community (or walled community) is a form of residential community or housing estate containing strictly controlled entrances for pedestrians, bicycles, and automobiles, and often characterized by a closed perimeter of walls and fences. Historically, cities have built defensive city walls and controlled gates to protect their inhabitants, and such fortifications have also separated quarters of some cities. Today, gated communities usually consist of small residential streets and include various shared amenities. For smaller communities, these amenities may include only a park or other common area. For larger communities, it may be possible for residents to stay within the community for most daily activities. Gated communities are a type of common interest development, but are distinct from intentional communities. Given that gated communities are spatially a type of enclave, Setha M. Low, an anthropologist, has argued that they have a negative effect on the net social capital of the broader community outside the gated community. Some gated communities, usually called "guard-gated communities", are staffed by private security guards and are often home to high-value properties, and/or are set up as retirement villages. Some gated communities are secure enough to resemble fortresses and are intended as such. Cruise ships function as floating gated communities. Features Besides the services of gatekeepers, many gated communities provide other amenities. These may depend on a number of factors including geographical location, demographic composition, community structure, and community fees collected. When there are sub-associations that belong to master associations, the master association may provide many of the amenities. In general, the larger the association the more amenities that can be provided. Amenities also depend on the type of housing. For example, single-family-home communities may not have a common-area swimming pool, since individual home-owners have the ability to construct their own private pools. A condominium, on the other hand, may offer a community pool, since the individual units do not have the option of a private pool installation. Typical amenities offered can include one or more: Swimming pools Bowling alleys Tennis courts Community centres or clubhouses Golf courses Marina On-site dining Playgrounds Exercise rooms including workout machines Spa Coworking spaces Around the world In Brazil, the most widespread form of gated community is called "condomínio fechado" (closed housing estate) and is the object of desire of the upper classes. Such a place is a small town with its own infrastructure (reserve power supply, sanitation, and security