At that time Judah besieged the Syrians who were posted in the citadel. They, being sore pressed with famine and want of all things, sent messengers to the king to implore assistance. Accordingly, Eupator came to their aid with a hundred thousand infantry and twenty thousand cavalry, while elephants marched in front of his line, causing immense terror to the onlookers. Then Judah, abandoning the siege, went to meet the king, and routed the Syrians in the first battle. The king begged for peace, which, because he, with his treacherous disposition, made a bad use of, vengeance followed his treachery.
For Demetrius, the son of Seleucus, who, we have said above, was handed over as a hostage to the Romans, when he heard that Antiochus had departed, begged that they would send him to take possession of the kingdom. And when this was refused to him, he secretly fled from Rome, came into Syria, and seized the supreme power, having slain the son of Antiochus, who had reigned one year and six months. It was during his reign that the Jews first begged the friendship of the Roman people, and alliance with them; and the embassy to this effect having been kindly received, they were, by a decree of the senate, styled allies and friends.
In the meantime Demetrius was, by means of his generals, carrying on war against Judah. And first the army was led by a certain man named Bacchides, and by Alcimus, a Jew; Nicanor, being afterwards placed at the head of the war, fell in battle. Then Bacchides and Alcimus, recovering power, and having increased their forces, fought against Judah. The Syrians, turning out victorious in that battle, cruelly abused their victory. The Hebrews elect Jonathan, the brother of Judah, in his place.
In the meantime, Alcimus, after he had fearfully desolated Jerusalem, dies; Bacchides, being thus deprived of his ally, returns to the king. Then, after an interval of two years, Bacchides again made war upon the Jews, and being beaten, he begged for peace. This was granted him certain conditions, to the effect that he should give up the deserters and prisoners, along with all that he had taken in war.
Source: Sacred History (New Advent)