might have happened had Rome not refused to conquer eastward of the Rhine? Who can say that a single mighty sea-power, wholly Latinised as far as the Black and Baltic Seas, would not have commanded the world from its peninsular base? But Classical Rome was primarily a Mediterranean and not a peninsular power, and the Rhine-Danube frontier must be regarded as demarking a penetration from the Mediterranean coast rather than as the incomplete achievement of a peninsular policy.
It was the 'opening' again of the seas on either hand which first compacted Europe in the peninsular sense. Reaction had to be organised, or the pressures from north and south would have obliterated Christendom. So Charlemagne erected an Empire astride of the Rhine, half Latin and half German by speech, but wholly Latin ecclesiastically. With this Empire as base the Crusades were afterwards undertaken. Seen in large perspective at this distance of time, and from the seaman's point of view, the Crusades, if successful, would have had for their main effect the 'closing' once more of the Mediterranean Sea. The long series of these wars, extending over two centuries, took two courses. On the one hand, fleets were sent out from
