The formation and subsequent breakup of the supercontinent Pangaea has dominated Earth's evolution for the last 320 million years. Although its configuration at the time of breakup is widely accepted, there remains uncertainty about its configuration at the time of its amalgamation. The classic Pangaea-A model, widely known as "Wegenerian" configuration, implies that Pangaea did not deform internally between amalgamation and breakup. Palaeomagnetic studies suggest the possibility of a Pangaea-B configuration, in which Gondwana was located about 3000 km farther east relative to Laurasia compared its location in Pangaea-A. Here, we provide firm evidence of an Iberian-Appalachian connection in the Late Pennsylvanian (307-299 Ma) which confirms a Pangaea-A configuration for the relative locations of Gondwana and Laurasia in the late Palaeozoic, negating the possibility of Pangaea-B at that time. This evidence is based on palaeobotanical and biostratigraphic findings recently documented in the Carboniferous successions of Iberia (Douro Basin, Portugal). These new findings also precisely constrain the timing of uplift of the Appalachian and Iberian (Variscan) orogens and climatic changes during the amalgamation of Pangaea and final closure of the Rheic Ocean.