This paper argues that colleges anchor their communities by developing knowledge and skills within their region; establishing links and exchanges outside the region; contributing to civic, political, cultural, and social activities and networks in their region; developing facilities and amenities used by the community; and, contributing to their region's economic activity. Particularly important are colleges' development of shared, collective or communal capacities, since these develop communities as communities, rather than individuals and organisations as discrete members of communities. We use Durkheimian sociology and critical realism to re-interpret the concept of agglomeration which we borrow from economics to trace the evolution of the concept of anchor institutions. Agglomeration is a particular type of emergence of phenomena from the interaction of components, where the whole is greater than the sum of its parts. We argue that colleges benefit their communities through the agglomeration of activities and organisations, from which emerge distinctive characteristics of their communities. This leads to the economic, social, and cultural benefits of agglomeration or clustering of activities within a geographic area. The accumulation of knowledge and knowledgeable people in communities increases the sharing of knowledge between people and organisations, and facilitates the generation and diffusion of knowledge.