r upon the Duke of Tver, and after a seven
years' struggle (1368-1375), compelled him to renounce his claims.

Dmitri was summoned before the Khan, in 1371. He went but what he saw
at Sarai convinced him that the Tartars were no longer able to uphold
their authority. He did not hesitate to engage in a struggle with
Riazan, although it was supported by a Tartar army. Thereafter, when
orders arrived from the khan, Dmitri ignored them. In 1376, he sent a
large army to Kazan on the Volga, and forced two Mongol chiefs to pay
tribute. Two years later, in 1378, a battle was fought between Dmitri
and one of Mamai's generals in Riazan, when the Tartars were defeated,
which made the grand duke exclaim: "Their time is come, and God is
with us!" The khan sent an army to ravage Riazan, and made
preparations to reestablish his authority at Moscow.

To make sure of success, Mamai took two years to collect an immense
army and to mature his plans. This could not remain secret to the
Russians, who, aroused by Dmitri, laid aside their private feuds to
make common cause against the infidels. A large number of dukes
assembled at Moscow, and even the Lithuanians promised to send (p. 091)
troops to Kostroma where the Russian army was gathering. The
Metropolitan assured Dmitri of the victory, and sent two monks to go
with the troops. Making the sign of the Cross on their cowls, he said,
"Behold a weapon which faileth never!"

Russia was united against the Mongol; all the dukes, with the
exception of those of Tver and Riazan, lent their aid. These two
dreaded Moscow's power, and the Duke of Riazan tried to conclude an
alliance with Jagellon of Lithuania and Mamai.

Dmitri, at the head of an army estimated at 150,000 men, marched
through Riazan to the Don where the Tartars were drawn up, awaiting
the reinforcements of their ally Jagellon, who was still fifteen
leagues distant. Dmitri resolved to fight the Tartars before a
junction could be effected. He crossed the Don and met the enemy on
the plain of Koulikovo,--the Field of the Woodcocks,--where a furious
battle was fought. It was decided by a sudden attack upon the Tartars
from an ambush, which threw them into a panic. The Tartars were
routed; Mamai's camp, his chariots and camels, were all captured.
Dmitri was found in a swoon from loss of blood. He was surnamed
Donskoi, in honor of this victory. (1380.)

It seemed as if the end of the Mongol yoke had come, when another
great leade