The open country was swept bare by the Slavs: the towns resisted better, for neither Slav nor Avar was skilled in siege operations. Relying upon the fortified towns as his base the great general Priscus, whom Maurice placed in command, was able to keep his ground along the Danube, and to perform many gallant exploits. He even crossed the river and attacked the Slavs and Avars in their own homes beyond it; but it was to no effect that he burnt their villages and slew off their warriors. He could not protect the unarmed population in the open country within the Roman boundary, and the girdle of fortresses along the Danube soon covered nothing but a wasted region, sparsely inhabited by Slavs. The limit of Roman population had fallen back to the line of the Balkans, and even to the south of it, and the Slavs were ever slipping across the Danube in larger and larger numbers, despite the garrisons along the river which were still kept up from Singidunum [Belgrade] to Dorostolum [Silistria]. The misfortunes of the Avaric and Slavonic war were the cause of the fall of the Emperor Maurice. He had won some unpopularity by his manifest inability to stem the tide of the barbarian invasion, and more by an act of callousness, of which he was guilty in 599. The Chagan of the Avars had captured 15,000 prisoners, and offered to release them for a large ransom. Maurice—whose treasury was empty—refused to comply, and the Chagan massacred the wretched captives. But the immediate cause of the emperor’s fall was his way of dealing with the army. He was unpopular with the soldiery, though an old soldier himself, and did not possess their respect or confidence. Yet he was an officer of some merit and had written a long military treatise called the “Strategicon,” which was the official handbook of the imperial armies for three hundred years. Maurice sealed his fate when, in 602, he issued orders for the discontented army of the Danube to winter north of the river, in the waste marshes of the Slavs. The troops refused to obey the order, and chased away their generals. Then electing as their captain an obscure centurion, named Phocas, they marched on Constantinople. Maurice armed the city factions, the “Blues” and “Greens,” and strove to defend himself. But when he saw that no one would fight for him, he fled across the Bosphorus with his wife and children, to seek refuge in the Asiatic provinces, where he was less unpopular than in Europe. Soon he was pursued by orders of Phocas, whom the army had now saluted as emperor, and caught at Chalcedon. The cruel usurper had him executed along with all his five sons, the youngest a child of only three years of age. Maurice died with a courage and piety that moved even his enemies, exclaiming with his last breath, “Thou art just, O Lord, and just are thy judgments!” X. THE DARKEST HOUR.