Ergo humanum genus bene se habet et optime, quando secundum quod
potest Deo adsimilatur. Sed genus humanum maxime Deo adsimilatur
quando maxime est unum; vera enim ratio unius in solo illo est.
Propter quod scriptum est: 'Audi, Israel, Dominus Deus tuus unus
est'. DANTE, _De Monarchia_, i. viii.


I

He who shuts his eyes to-day to make a mental picture of the world sees
a globe in which the mass of Asia, the bulk of Africa, and the length of
America vastly outweigh in the balance the straggling and sea-sown
continent of Europe. He sees all manner of races, white and yellow,
brown and black, toiling, like infinitesimal specks, in every manner of
way over many thousands of miles; and he knows that an infinite variety
of creeds and civilizations, of practices and beliefs--some immemorially
old, some crudely new; some starkly savage, and some softly
humane--diversify the hearts of a thousand million living beings. But if
we would enter the Middle Ages, in that height and glory of their
achievement which extended from the middle of the eleventh to the end of
the thirteenth century, we must contract our view abruptly. The known
world of the twelfth century is a very much smaller world than ours, and
it is a world of a vastly greater unity. It is a Mediterranean world;
and 'Rome, the head of the world, rules the reins of the round globe'.
From Rome the view may travel to the Sahara in the south; in the east to
the Euphrates, the Dniester, and the Vistula; in the north to the Sound
and the Cattegat (though some, indeed, may have heard of Iceland), and
in the west to the farther shores of Ireland and of Spain. Outside these
bounds there is something, at any rate to the east, but it is something
shadowy and wavering, full of myth and fable. Inside these bounds there