In this paper we examine the increasing criminalisation by states and the EU of citizen networks that have mobilised across Europe for supporting migrants in transit. Through these transnational solidarity practices a sort of infrastructure of migrant support has been built. The paper focuses on ‘crimes of solidarity’ that have taken place in France and in Italy and argues that the criminalisation of individuals which build solidarity connections across borders paradoxically constitutes a radical challenge to Europe’s principles of citizens’ solidarity across borders. The infrastructure of migrant support enacts a form of Europeanisation of citizens’ practices that states and local authorities try instead to undermine. The paper moves on by focusing on the ambivalences of the expression ‘smuggling activities’, which is increasingly being used to name individuals who help migrants to cross or to stay without making any economic profit from that. The essay considers the frictions between local, national and European authorities in tolerating or criminalising citizens that act in solidarity with the migrants, bringing humanitarian help and building material channels for safe passages. The final part of the paper reads the moment of crimes of solidarity in terms of a genealogy of European borders. It argues that one consequence of the criminalisation of solidarity is that new hybrid forums concerning migration, citizenship and borders questions are emerging. These arise, for example, when citizens are prosecuted for acts of assistance. Their trials have potential to become public scenes and spaces of counter-politics where it is not only the citizen but Europe that is in the dock. While some have argued that criminalisation and humanitarianism closes down the politics of European borders, we argue that it may allow for unexpected political opportunities.