There was no formal border between English and French territory. Many landholders owned a patchwork of widely separated estates, perhaps owing fealty to a different overlord for each, or holding some rights from the French Crown as the monarch and others from the English Crown as their liege lord. Each small estate was likely to have a fortified tower or keep, with larger estates having castles. Fortifications were also constructed at transport choke points, to collect tolls and to restrict military passage; fortified towns grew up alongside all bridges and most fords over the many rivers in the region.