Roman power, both in occupied Britain and in Rome. Frontiers in the early empire were based more on natural features or fortified zones with a heavy military presence. Military roads or limes often marked the border, with forts and signal towers spread along them and it was not until the reign of Domitian that the first solid frontier was constructed, in Germania Superior, using a simple fence. Hadrian expanded on this idea, redesigning the German border by ordering a continuous timber palisade supported by forts behind it. Although such defences would not have held back any concerted invasion effort, they did physically mark the edge of Roman territory and went some way to providing a degree of control over who crossed the border and where. Hadrian reduced Roman military presence in the territory of the Brigantes and concentrated on building a more solid linear fortification to the north of them. This was intended to replace