This paper focuses on the relationships between Spanish and Portuguese geologists during the second half of the nineteenth century, and their cooperation in Iberian and European scientific projects, with particular emphasis on the geological map of Europe, whose publication, in 1896, was a symbolic demonstration of Prussia's capacity to dominate the whole continent. We argue that the period from 1857 to 1896 defined a cycle in the relationships between Spanish and Portuguese geologists marked by common generational aspirations, converging intellectual pursuits (...) and political and ideological affinities associated with the intellectual and political movements which stirred the cultural and political life of both Iberian countries. At a time when the unification of Iberia was being discussed on both sides of the Spanish–Portuguese border, this background favoured and shaped cooperation between the Spanish and Portuguese Geological Surveys, in particular their participation in the geological map of Europe, which, nevertheless, coincided with the end of this cycle in Iberian geology. (shrink)