Nerva adopted Trajan, who proved the most accomplished prince in all history.
His reign blessed the empire with more prosperity and true glory than it had ever enjoyed before.
- an admirable statesman
- a most accomplished general
The native sweetness of his disposition inclined him to universal humanity.
His unclouded penetration guided him through the best and purest tracts of government.
He was actuated by a noble soul, to whose embellishment every virtue had contributed.
His conduct was free from all extremes, and his amiable qualities were tempered with such exact proportion that the brightness of one was never lost in the lustre of another.
To sum up all, he was the best qualified of mankind, to do honour to human nature, and to represent the divinity on earth.
He accomplished Cæsar’s project of invading the Parthians, and was very successful in his wars with that mighty people; any monarch but himself would have sunk under the weight of such an enterprize, where danger was always present, and from whence the source of his necessary supplies was at a vast distance; in a word, where he could not be sure of victory itself would save him from destruction.
The difficulty consisted in:
- the location of the 2 empires, and
- the military discipline of both nations.
If he directed his march through Armenia towards the sources of Tygris and Euphrates, he was sure to be incommoded with a mountainous and impracticable country, through which no convoy of provision could pass, so that the army would be half destroyed before they could penetrate into Media * .
On the other hand, if he should strike out a lower tract towards the south, through Nisibis, he would find himself bewildered in a ghastly desart that separated the two empires;
Iif he intended to proceed still lower, and march through  Mesopotamia, he was then to cross a large country that was either uncultivated or laid under water.
The Tigris and Euphrates flowed from north to south. He could not gain a passage into the country without quitting those rivers, which, if he did, he must inevitably perish.
As to the manner practised by the two nations in making war, the strength of the Romans consisted in their infantry, which was the most firm and best disciplined body of soldiers in the world.
The Parthians on the contrary, had no infantry. Their horses were admirable, and always combated at such a distance, as placed them out of the reach of the Roman army.
The javelin was seldom launched far enough to wound them.
Their own weapons consisted of a bow, and many formidable shafts.
They besieged an army instead of giving it battle.
They were pursued to no purpose in their flight, for that was the same with them as an engagement.
They carried off all the inhabitants of the country, and only left garrisons in their fortified places.
When these were taken, the conquerors were obliged to destroy them.
The Parthians likewise set fire to all the country that lay round the Roman army, and did not leave them the least blade of herbage.
They managed their wars in manner very much like that which is now practised on the same frontiers.
We may add to these disadvantages, that the Illyrian and German legions which were drawn out for this war, were no way capable to sustain it, * because the soldiers, who were accustomed to plentiful food in their own country, perished in these regions for want of many necessaries.
The Parthians by these means had accomplished that, for the preservation of their liberty, which had hitherto been impracticable to all other nations, against  the victorious power of the Romans= but they owed this advantage not to any resistless valour, but to their inaccessible situation.
- gave up the conquest of Trajan
- made Euphrates the boundary of his empire.
It was surprizing that the Romans, after such a series of war, should lose nothing but what they wanted to quit.
Thus they resembled the ocean, whose expansion is never lessened but when it retires of itself.
This conduct of Adrian occasioned great dissatisfactions among the people.
It was recorded in the sacred book of that nation* that when Tarquin intended to build the capitol, he found the place most commodious for his purpose filled with the statues of other deities, upon which he employed his skill in augury to discover if they were inclinable to resign their places to Jupiter, and they all consented, except Mars, Hebe, and Terminus.
This gave birth to 3 religious opinions:
- Mars would never resign his place to any other being
- The Roman youth would be always invincible
- The Roman god Terminus would never recede from his station
The contrary of which was however verified in the reign of Adrian.