Twice, almost unconsciously (for there is no Mediterranean in the index), a contributor to the compilation of essays entitled Britain and Ireland, 900–1300. Insular Responses to European Change remarks with surprise that the commerce found in the high Middle Ages in the Irish Sea reminds him of the Mediterranean further south (see pp. 42, 64). It is not the first time this improbable comparison has been made. About 1200, Gerald of Wales, a prolific writer and ambitious ecclesiastical careerist, had already made such a juxtaposition, though for him what was most striking was how different the two bodies of water were. For Gerald, the true Mediterranean was easier to navigate in winter and less subject to dangerous tides in all seasons than the treacherous Irish Sea.Giraldus Cambrensis, Topographia Hibernica, 2.1, 2.3; Expugnatio Hibernica, 1.2, 1.35. Both texts are available in convenient English translation: The History and Topography of Ireland (Hamondsworth, Middlesex: Penguin, 1982). Still, Gerald's texts brim over with references to ships and people traversing the waters of the Irish Sea, which suggests that sea was more like the Inner Sea between Europe, Africa, and Asia than Gerald admitted. After all, both seas are enclosed by land, both are relatively small (though the Mediterranean is much deeper and about ten times bigger than the Irish Sea), and both have long facilitated communication. It is thus less surprising to find that in Peter Brown's mesmerizing account of The Rise of Western Christendom the importance of the Irish Sea for Ireland's unique early medieval development is emphasized by calling this appendage of the North Atlantic a “Celtic Mediterranean of the north,” in other words, it is a manageable body of water through which communication was easy enough for “Celtic” economic and cultural unity to arise along its shores.P. Brown, The Rise of Western Christendom (Cambridge, MA: Blackwell, 1996), 81. Brown was, perhaps unwittingly, following a tradition among British geographers. H. MacKinder, in Britain and the British Seas (New York: D. Appleton & Co., 1902, 20), already spoke of the Irish Sea as a “British Mediterranean.” Between the fifth and ninth centuries, when medieval Irish culture reached an apogee, the Irish Sea was bustling, conveying abundant goods and ideas rather as happened in the Romans' “very own sea” (mare nostrum) in the relaxed centuries of Roman peace. Some early medieval writers who had a more direct experience of the “Irish Ocean” (Oceanus Hibernicus) might have dissented from Brown's image of tranquil navigability, but Brown is, nevertheless, right.The Voyage of St. Brendan (available in English in The Age of Bede, Harmondsworth, Middlesex: Penguin, 1988), perhaps the most famous account of medieval Irish navigation, presents the seas as highly unpleasant, dangerous places. Nor should it be forgotten that the early medieval Irish ascetic practice of abandoning oneself to the sea was considered a penance. Many sailed the waters between Britain and Ireland. St. Patrick is only the most famous to have completed the voyage (at least three times) in the postclassical centuries, bringing with him a typical Mediterranean export, Christianity. Mediterranean pottery and that distinctive Mediterranean machine, the watermill, crop up often enough in medieval sites in Ireland to prove the Irish Sea was no barrier.See C. Rynne, “Hydropower in Medieval Ireland,” in Working with Water in Medieval Europe, ed. P. Squatriti (Leiden: Brill, 2000), 1. In fact, borrowing a neologism from a fresh and stimulating survey of the pre-modern Mediterranean, we may say the Irish Sea enjoyed great “connectivity” in pre-industrial times.<+>5 This means that, as Brown postulated, beyond the transport of luxuries over long distances in the Irish Sea, many small-scale, short-range exchanges took place along its shores, across its waters, in its harbors, and quite far inland from its coast. Redistribution on such a scale was possible only thanks to the sea waters. The sea wove together a tapestry of interdependence, forming a true economic and cultural region.