The Illyrian frontier was covered by a line of castles and fortresses; and though the greatest part of them consisted only of a single tower, with a small garrison, they were commonly sufficient to repel or to intercept the inroads of an enemy who was ignorant of the art and impatient of the delay of a regular siege. But these slight obstacles were instantly swept away by the inundation of the Huns. They destroyed, with fire and sword, the populous cities of Sirmium and Singidunum, of Ratiaria and Marcianopolis, of Naissus and Sardica; where every circumstance of the discipline of the people and the construction of the buildings had been gradually adapted to the sole purpose of defence. The whole breadth of Europe, as it extends above five hundred miles from the Euxine to the Hadriatic, was at once invaded and occupied and desolated by the myriads of Barbarians whom Attila led into the field. The public danger and distress could not, however, provoke Theodosius to interrupt his amusements and devotion or to appear in person at the head of the Roman legions. But the troops which had been sent against Genseric were hastily recalled from Sicily; the garrisons on the side of Persia were exhausted; and a military force was collected in Europe, formidable by their arms and numbers, if the generals had understood the science of command and their soldiers the duty of obedience. The armies of the Eastern Empire were vanquished in three successive engagements; and the progress of Attila may be traced by the fields of battle. The two former, on the banks of the Utus and under the walls of Marcianapolis, were fought in the extensive plains between the Danube and Mount Haemus. As the Romans were pressed by a victorious enemy, they gradually and unskilfully retired toward the Chersonesus of Thrace; and that narrow peninsula, the last extremity of the land, was marked by their third, and irreparable, defeat. By the destruction of this army Attila acquired the indisputable possession of the field. From the Hellespont to Thermopylae, and the suburbs of Constantinople, he ravaged, without resistance and without mercy, the provinces of Thrace and Macedonia. Heraclea and Hadrianople might, perhaps, escape this dreadful irruption of the Huns; but the words, the most expressive of total extirpation and erasure, are applied to the calamities which they inflicted on seventy cities of the Eastern Empire. Theodosius, his court, and the unwarlike people were protected by the walls of Constantinople; but those waits had been shaken by a recent earthquake, and the fall of fifty-eight towers had opened a large and tremendous breach. The damage indeed was speedily repaired; but this accident was aggravated by a superstitious fear, that heaven itself had delivered the imperial city to the shepherds of Scythia, who were strangers to the laws, the language, and the religion of the Romans.