Tacitus writes that Agricola made special military dispositions on that side of Britain which faces Ireland; and this he did more through hope than through fear, that is to say, rather in view of conquest than of protection. Ireland, he says, is situate between Britain and Spain. It is of smaller area than Britain. In soil and climate and in the character of its inhabitants it differs little from Britain. Its inland parts are little known, its approaches and harbours are better known through commerce and merchants. Agricola received one of its petty kings who had been expelled in a revolt and kept him, under the guise of friendship, against a suitable opportunity. From Agricola, I, says Tacitus, have often heard that Ireland could be conquered and held by a single legion with a moderate force of auxiliaries, and that this would be of advantage as regards Britain, if the Roman military power were established everywhere and freedom, as it were, were put out of sight. Later he writes that Agricola had led his forces to a point close to the Irish Sea when he was brought back by an outbreak among the Brigantes and thought it better to solidify the conquests he had already made than to undertake a new conquest. The next writer in point of date is Ptolemy the Geographer, who flourished in the middle of the second century. Ptolemy names sixteen peoples, tribes or states, and gives their relative positions on the Irish coast. He names no people or state away from the coast. About half of the names can be authenticated from other sources. The others have been the subject of much fruitless conjecture. It is noteworthy that all the authenticated names belong to the eastern and southern coasts and that the names on the northern and western coasts are still names and nothing more. This shows that Ptolemy's information came from sea-going traders. The northern and western coasts of Ireland are among the most stormy in the world and must have been avoided in those days by ocean-going craft. Ptolemy names several estuaries, and from Irish writings we know that in early times estuaries were the favourite havens. Ships could run in by the main channel and could be grounded without injury on the sandy tidal banks. Several "cities" are likewise named by Ptolemy. These, no doubt, were places of assembly or royal towns--"oppida," like Tara and Emania. None of them can be identified with any approach to certainty. Two bear the name _Regia polis_, and this I think is taken from Latin, meaning "royal city."