Architecture has shaped in the past and is still shaping now and will shape the cities in the future. Especially in historical towns people can perceive different layers of architectural concepts of different architects from past to the future. In the past, the number of layers that influences cognition of man was fewer than that of nowadays. Today we see lots of environmental elements that interfere with man’s reading the milieu. As these elements increase people become much more selective to find out what they need. This selection procedure becomes “baiting” data from a chaotic sea of information. In addition to this chaos we as architects mostly try to give different messages and feelings to citizens. In such a milieu, people try to find easier way of selection, so mostly the innocent environmental shaping effort of the designer is ignored. But to get rid of this oblivion, for a sustainable city life and comfort of man’s mind, this flow of information must be organized by associative work of architects, urban planners and politicians. Aim must be the organization of the legibility of environment. In macro city scale the legibility of the environment is related to the geometrical formation of cityscape such as landmarks, nodes, districts, roads and borders. But in micro scale for example; in a part of a city such as a downtown square, the factors that affect the legibility changes according to space. Also in addition to these factors cultural and social symbolic elements and the complexity of stable and mobile elements can affect the cognitive map of that place in man’s mind. The sustainability of a city is only possible with the revitalization of the main centers. Istanbul is the biggest metropolis in Turkey. Its cosmopolite citizen’s structure is reflected to building pattern. This confusion is mirrored to the most important square: Taksim, Istanbul. Complexity is a dominant legibility factor and must be handled immediately for the future image of the New Millennium City of Culture: Istanbul. This paper aims to find out complexity factors affecting the legibility of Taksim Square with a case study and try to find out some suggestions for a future work studying in accordance with citizens of Istanbul