This paper discusses the story of a generous popular mobilisation that made possible a peculiar experience of transnational cooperation since the early 1970s. That is, the campaigns in solidarity with Mozambican anticolonial resistance that made the small town of Reggio Emilia (Italy) a key place in the processes of Lusophone Africa decolonization, to the point that an oftentold anecdote reports that many Mozambican people sympathetic with anti-colonialist organisation Frelimo believed that Reggio Emilia was the 'capital' of Italy. Indeed, it was mostly from the Emilian town that concrete aid arrived from Italy to Frelimo's clandestine guerrilla bases between Tanzania and Northern Mozambique. Based on the exceptional archives surviving in Reggio, which abundantly document the Reggio-Africa solidarity experience showing that it was not limited to Mozambique, and on original interviews with surviving protagonists, this paper extends and connects for the first time literature on city diplomacy with scholarship on critical, subaltern and liminal geopolitics of decolonization. I especially argue for giving more consideration to a 'radical city diplomacy', which provides examples for constructing geopolitical challenges form below to the state and the territorial models that have dominated mainstream geopolitics hitherto.