After his careful survey of the Rhine end of the great defensive barrier, Trajan proceeded to consider it and plan it from the Danube. From the age of Tiberius onward, the Romans possessed the whole southern bank of the river from its source to the Euxine. But the precarious tenure of their possession, had been deeply impressed on them by the disasters and humiliations they had undergone in these districts during the reign of Domitian. A prince had arisen among the Dacians, Decebalus by name, worthy to be placed at the head of all the great barbarian antagonists of Rome. Like Maroboduus, he was able to combine the forces of tribes commonly hostile to each other, and his military ability almost went the length of genius. After he had swept the province of Moesia bare, he was defeated by one of Domitian's lieutenants, but the position of affairs on the Danubio-Rhenish border was still so threatening, that the emperor was glad to conclude a treaty which conferred extraordinary advantages on his foe. Not only did the Romans stipulate to pay to Decebalus an annual subsidy, which he must have regarded as a tribute, but they agreed to supply him with engineers and craftsmen skilled in all kinds of construction, but particularly in the erection of fortifications and defensive works. During the nine or ten years which had elapsed since the conclusion of this remarkable treaty, the Dacian prince had immensely strengthened the approaches to his kingdom from the Roman side. He had also equipped and drilled his formidable army after the Roman fashion. It was impossible for a soldier like Trajan to endure the conditions laid down by Domitian; but the conquest of Dacia had become one of the most formidable tasks that had ever confronted the Empire. Trajan, no doubt, planned a war before he left the Danube for Rome late in 99.