was to move westwards from Asia into Europe, and this they did at
considerable and irregular intervals, though in alarming and apparently
inexhaustible numbers, roughly from the fourth till the fourteenth
centuries. The distance was great, but the journey, thanks to the flat,
grassy, treeless, and well-watered character of the steppes of southern
Russia which they had to cross, was easy. They often halted for
considerable periods by the way, and some never moved further westwards
than Russia. Thus at one time the Bulgars settled in large numbers on the
Volga, near its confluence with the Kama, and it is presumed that they
were well established there in the fifth century. They formed a community
of considerable strength and importance, known as Great or White Bulgaria.
These Bulgars fused with later Tartar immigrants from Asia and eventually
were consolidated into the powerful kingdom of Kazan, which was only
crushed by the Tsar Ivan IV in 1552. According to Bulgarian historians,
the basins of the rivers Volga and Don and the steppes of eastern Russia
proved too confined a space for the legitimate development of Bulgarian
energy, and expansion to the west was decided on. A large number of
Bulgars therefore detached themselves and began to move south-westwards.
During the sixth century they seem to have been settled in the country to
the north of the Black Sea, forming a colony known as Black Bulgaria. It
is very doubtful whether the Bulgars did take part, as they are supposed
to have done, in the ambitious but unsuccessful attack on Constantinople
in 559 under Zabergan, chief of another Tartar tribe; but it is fairly
certain that they did in the equally formidable but equally unsuccessful
attacks by the Slavs and Avars against Salonika in 609 and Constantinople
in 626.

During the last quarter of the sixth and the first of the seventh century
the various branches of the Bulgar nation, stretching from the Volga to
the Danube, were consolidated and kept in control by their prince Kubrat,