Portugal comprises distinct geographical zones, a mountainous in the north, a lowland in the south, the dividing line being the river Tagus. The principal urban centres, Coimbra, Lisbon, Oporto and Silves, were riverside communities, as were many lesser settlements with a history of fishing, shipbuilding and maritime enterprise. The consciousness of Portuguese nationalism, portuguesismo, awoke with war: the battle of Aljubarrota, elaborately reported by chroniclers and further exalted by myth, marked its birth. Of all the elements forming Portuguese political structures, the royal office was the most important. Joäo I secured for the crown in 1402, when all cities came to be recognised as belonging to the crown; only Braga, seat of the primate of Portugal, eventually had its former independence restored, reverting to archiepiscopal control. The two reigns of Joäo I and Duarte reveal coherent continuity, a result of the fact that Duarte was associated with his father's rule in the last third of the latter's very long reign.