Walk around Colombia’s second city Medellín and you are never far from a bank, office or shop that is controlled in some way or other by the Grupo Empresarial Antioque?o, the most powerful alliance of companies in the nation.

On street corners, there are branches of Bancolombia, the country’s biggest bank. Within gleaming glass towers sit the headquarters of Grupo de Inversiones Suramericana, Colombia’s largest financial conglomerate, which holds stakes in banking, insurance, pensions and asset management. Buy food in the city’s supermarkets and the chances are it is produced by Grupo Nutresa, which started life as a Medellín chocolate-maker over a century ago and is now one of Latin America’s biggest processed food firms.

All these companies, and over 100 more, are part of the GEA, a network of firms in Medellín and the surrounding department of Antioquia linked to one another through a complex web of cross-shareholdings and family ties. Between them they account for over half the value of the Colcap, the main index of the Colombian stock exchange.