"...a man [Mithridates VI] about whom one cannot speak except with concern nor yet pass by in silence; he was ever eager for war, of exceptional bravery, always great in spirit and sometimes in achievement, in strategy a general, in bodily prowess a soldier, in hatred to the Romans a Hannibal."
Velleius Paterculus, Compendium of Roman History (II.18.1)
In 89 BC, while Rome was preoccupied with the Social War against her Italian allies, Mithridates VI (Eupator), king of Pontus on the southern shore of the Black Sea, annexed neighboring Cappadocia and Bithynia. In The Mithridatic Wars (III.10-21), Appian relates that Manius Aquillius, as head of a Roman commission to Asia, ordered that both kings be restored. They were, but it then was suggested that their debt to Rome could be repaid if Mithridates' own kingdom were invaded and plundered. Nicomedes IV of Bithynia reluctantly did so, because he "had agreed to pay a large sum of money to the generals and ambassadors for restoring him to power, which he still owed, together with other large sums which he had borrowed on interest from the Romans in their suites, and for which they were dunning him." It was to be a disastrous miscalculation on the part of Aquillius and marked the beginning of the First Mithridatic War.
Mithridates retook Cappadocia and Bithynia, defeating Nicomedes at the river Amnias. Fighting against chariots armed with scythes on the wheels, the army was "terrified at seeing men cut in halves and still breathing, or mangled in fragments, or hanging on the scythes. Overcome rather by the hideousness of the spectacle than by loss of the fight, fear disordered their ranks." Mithridates then swept into Phrygia and the Roman province of Asia. Aquilius, who so ill-advisedly had precipated the war without ratification from the Senate, fled the mainland but was given up by the citizens of Mytilene. Ridiculed and paraded on an ass, he eventually was executed, relates Appian, when "Mithridates poured molten gold down his throat, thus rebuking the Romans for their bribe-taking."
In 88 BC, in a measure of the hatred felt for the Romans in Asia, Mithradates "wrote secretly to all his satraps and city governors that on the thirtieth day thereafter they should set upon all Romans and Italians in their towns, and upon their wives and children and their freedmen of Italian birth, kill them and throw their bodies out unburied, and share their goods with King Mithridates" (III.22). Tens of thousands were massacred: Valerius Maximus (XI.2.4) records 80,000 deaths, Plutarch (Sulla, XXIV.4), 150,000, in what has been called the Asian or Ephesian Vespers (after the Sicilian Vespers of 1282, in which the native Sicilians killed virtually all the ruling French on the island). Mithridates now was sovereign of all Asia Minor.
As the Romans learned to contend with Mithridates' war chariots, their terror abated.
"As a chariot of this sort does not always meet with plain and level ground, the least obstruction stops it. And if one of the horses be either killed or wounded, it falls into the enemy's hands. The Roman soldiers rendered them useless chiefly by the following contrivance: at the instant the engagement began, they strewed the field of battle with caltrops, and the horses that drew the chariots, running full speed on them, were infallibly destroyed. A caltrop is a machine composed of four spikes or points arranged so that in whatever manner it is thrown on the ground, it rests on three and presents the fourth upright."
Flavius Vegetius Renatus: De Re Militari (III.24)
References: Appian: Roman History (1912) translated by Horace White (Loeb Classical Library); Velleius Paterculus: Compendium of Roman History (1924) translated by Frederick W. Shipley (Loeb Classical Library); Plutarch: Parallel Lives (1916) translated by Bernadotte Perrin (Loeb Classical Library); "Mithridates" by John G. F. Hind, in The Cambridge Ancient History (Vol. IX) (1994) edited by J. A. Cook, Andrew Lintott, and Elizabeth Rawson; The Foreign Policy of Mithridates VI Eupator, King of Pontus (1986) by B. C. McGing (Mnemosyne, Suppl. 89); Roman Foreign Policy in the East: 168 BC to AD 1 (1984) by A. N. Sherwin-White; Flavius Vegetius Renatus: The Military Institutions of the Romans (1767/1944) translated by Lieut. John Clark.