The best means of realising the extent of the Roman Empire in or about the year 64 is to glance at the map. It will be found to reach from the Atlantic Ocean to the Euphrates, from the middle of England—approximately the river Trent—to the south of Egypt, from the Rhine and the Danube to the Desert of Sahara. The Mediterranean Sea is a Roman lake, and there is not a spot upon its shores which is not under Roman rule. In round numbers the empire is three thousand miles in length and two thousand in breadth. Its population, which, at least in the western parts, was much thinner then than it is over the same area at present, cannot be calculated with any accuracy, but an estimate of one hundred millions would perhaps be not very far from the mark.                             Beyond its borders—sometimes too dangerously near to them and apt to overstep them—lay various peoples concerning whom Roman knowledge was for the most part incomplete and indefinite. Within its own boundaries the Roman government carefully collected every kind of information. Such precision was indispensable for the carrying out of those Roman principles of administration which will be described later. But of the nations or tribes beyond the frontiers only so much was known as had been gathered from a number of more or less futile campaigns, from occasional embassies sent to Rome by such peoples, from the writings of a few venturous travellers bent on exploration, from slaves who had been acquired by war or purchase, or from traders such as those who made their way to the Baltic in quest of amber, or to Arabia, Ethiopia, and India in quest of precious metals, jewels, ivory, perfumes, and fabrics.                             There had indeed been sundry attempts to annex still more of the world. Roman armies had crossed the Rhine and had twice fought their way to the Elbe; but it became apparent to the shrewd Augustus and Tiberius that the country could not be held, and the Rhine was for the present accepted as the most natural and practical frontier. In the East the attempts permanently to annex Armenia, or a portion of Parthia, had so far proved but nominal or almost entirely vain...