of the Danube, though they were always overrunning into Upper Moesia, the modern Serbia.  The Slavs, whose numbers were without doubt very large, gradually settled all over the country south of the Danube, the rural parts of which, as a result of incessant invasion and retreat, had become waste and empty.  During the second half of the sixth century all the military energies of Constantinople were diverted to Persia, so that the invaders of the Balkan peninsula had the field very much to themselves.  It was during this time that the power of the Avars reached its height.  They were masters of all the country up to the walls of Adrianople and Salonika, though they did not settle there.  The peninsula seems to have been colonized by Slavs, who penetrated right down into Greece; but the Avars were throughout this time, both in politics and in war, the directing and dominating force.  During another Persian war, which broke out in 622 and entailed the prolonged absence of the emperor from Constantinople, the Avars, not satisfied with the tribute extorted from the Greeks, made an alliance against them with the Persians, and in 626 collected a large army of Slavs and Asiatics and attacked Constantinople both by land and sea from the European side, while the Persians threatened it from Asia.  But the walls of the city and the ships of the Greeks proved invincible, and, quarrels breaking out between the Slavs and the Avars, both had to save themselves in ignominious and precipitate retreat.

After this nothing more was heard of the Avars in the Balkan peninsula, though their power was only finally crushed by Charlemagne in 799.  In Russia their downfall became proverbial, being crystallized in the saying, ‘they perished like Avars’.  The Slavs, on the other hand, remained.  Throughout these stormy times their penetration of the Balkan peninsula had been peacefully if unostentatiously proceeding; by the middle of the seventh century it was complete.  The main streams of Slavonic immigration moved southwards and westwards.  The first covered the whole of the country between the Danube and the Balkan range, overflowed into Macedonia, and filtered down into Greece.  Southern Thrace in the east and Albania in the west were comparatively little affected, and in these districts the indigenous population maintained itself.  The coasts of the Aegean and the great cities on or near them were too strongly held by the Greeks to be affected, and those Slavs who penetrated into Greece itself were soon absorbed by the local populations.  The still stronger Slavonic stream, which moved westwards and turned up north-westwards, overran the whole country down to the shores of the Adriatic and as far as the sources of the Save and Drave in the Alps.  From that point in the west to the shores of the Black Sea in the east became one solid mass of Slavs, and has remained so ever since.  The few Slavs who were left north of the Danube in Dacia were gradually assimilated by the inhabitants of that province, who were the descendants of the Roman soldiers and colonists, and the ancestors of the modern Rumanians, but the fact that Slavonic influence there was strong is shown by the large number of words of Slavonic origin contained in the Rumanian language.