Peter, surprised in Grodno, fled with 2000 men, while Karl with 600 entered the city.
When Peter learned that the bulk of the Swedish army was still five leagues distant he returned and tried to retake the town.
He was, however, fiercely beaten back, and the Swedes pursued the Russians through Lithuania and Minsk, towards the frontiers of Russia.
Karl, after clearing Lithuania of the forces of the Czar, intended to march towards the North and on Moscow, by way of Pskof.
The difficulties in his way were terrible; huge stretches of virgin forest, of desolate marsh, of barren deserts, lay between him and his objective. The only food that could be found was the winter stores of the peasants in the small tracks of cultivated land, which were buried underground; many of these had already been ravaged by the Muscovites, and in any case were insufficient for the Swedish army.
Karl, who was to be deterred neither by prudence, reason, nor fear of any kind, had provided bread for his men which they carried with them, and on this they had to support the ghastly hardships of the forced marches.
The heavy rains kept back even the indefatigable Swede. A road had to be made through the forest of Minsk, and it was early summer before Karl found himself once more face to face with Peter at Borissov.
The Czar waited with the main body of his forces to defend the river Bérézina; Karl, however, brought his troops across this river and marched on the Russians, who once more retreated, falling back on the Dneiper.
At Halowczin he defeated 20,000 Muscovites by traversing a marsh believed to be impassable, the King himself leading, with the water at times up to his shoulders.
After this decisive victory he pursued the Russians to Mohilew, on the frontiers of Poland; by the autumn he was chasing the Czar from Smolensk, on the Moscow road.