Nicomedes, more against his brother than his foreign enemies, now calls in the assistance of more powerful auxiliaries and enters into an alliance with the warlike Celts, or Gauls, who, under Leonnorius and Lutarius, had arrived on the opposite side of the Bosporus and are, at this time, engaged in the siege of Byzantium, 277 BCE.

Three Gallic tribes, twenty thousand strong, are initially recruited.

Having furnished them with the means of crossing into Asia, he first turns the arms of his new auxiliaries against Zipoetes II, whom he defeats and puts to death, and thus reunites the whole of Bithynia under his dominion.

Of the events that follow we have little information.

It is probable that the Celts subsequently assisted Nicomedes against Antiochus, but no particulars are recorded, either of the war or the peace that terminated it.

It appears, however, that Nicomedes was left in the undisturbed possession of Bithynia, which he continues to govern from this time until his death and which is to rise to a high degree of power and prosperity during his long and peaceful reign.

The Gauls, after discharging their military service to Bithynia, have by 276 settled in parts of Phrygia but continue to ravage and plunder on their own.

The deposed queen’s ambitious rival, widow to both Lysimachus and Keraunus, marries Ptolemy and adopts her children.

Sibling marriage, while scandalous to the Greeks, is a customary practice in Egypt.

The event shocks Greek public opinion but is celebrated by the Alexandrian court poets.

Philadelphoi (“Brother-Loving”) consequently is added to the names of Ptolemy and Arsinoe II.

Ptolemy, taking advantage of the difficulties of the rival kingdoms of the Seleucids and Antigonids, extends his rule in Syria, Asia Minor, and the Aegean at their expense and asserts at the same time his influence in Ethiopia and Arabia.

Egyptian embassies to Rome as well as to India reflect the wide range of Ptolemy's political and commercial interests.

The Egyptians invade northern Syria in 276, but Antiochus defeats Ptolemy, repels him, and secures an alliance with Ptolemy’s half brother, who rules Cyrene.

Macedon has had no central government for the past two years: three men had been offered the crown, but two of them were immediately dethroned and the third one, a nobleman named Sosthenes, had refused the supreme power.

Although the city-dwellers have had to fend for themselves, the Gauls lack the capacity to besiege towns.

Sosthenes has been able to harass Bolgius, who has returned with his loot to the region of modern Serbia.

The Macedonians in 276 acknowledge Antigonus king.

The despotic methods employed by Pyrrhus provoke a revolt of the Greek Sicilians, and in 276 (or early 275), he returns to Italy.

On his departure, the Syracusans appoint as commander of the troops his supporter Hiero, who strengthens his position by marrying the daughter of Leptines, the city's leading citizen.

Ptolemaic Egypt invades northern Syria in 276 BCE, but Antiochus defeats Ptolemy, repels him, and secures an alliance with Ptolemy’s half brother, who rules Cyrene.

The Gallic horde continues to plague western Anatolia until checked in 275 by Antiochus at the so-called Elephant Battle.

At this point, the Celts, called Galatae (Galatians) by third-century writers, settle, courtesy of Nicomedes of Bithynia and Mithridates of Pontus, in an area of northern Phrygia stretching from southwest to northeast through the central Anatolian plateau (the region will become known as Galatia (from Galli, the Latin word for Celts), there to serve as a buffer against the Seleucids.

Angora, one of their hillforts, is today Ankara, the Turkish capital.

Pyrrhus, after suffering heavy losses in a battle against Rome at Beneventum (Benevento) in 275, returns to Greece, while Rome puts down resistance in southern Italy.

The so-called First Syrian War erupts in 274-273 BCE between Antiochus and Ptolemy, a conflict partly occasioned by Seleucid support for the revolt of Magas, the Ptolemaic governor of Cyrene, who is linked to Antiochus by marriage to his daughter, Apame.

Ptolemy II conquers Tyre and renames the city Ptolemais.