Lysimachus, who has joined Cassander in the alliance against Antigonus, and Seleucus, holding on to a damaged Babylon and the eastern provinces, follow suit.

The immediate assumption of royal titles by their opponents ends the nominal unity of Alexander's empire, the partition of which, into five states, is now formally established.

Ptolemy, following Antigonus's vain attack of Egypt in 306-05, also assumes the title of king, as does Cassander in Macedonia.

Antigonus had sent Demetrius in 305 BCE to conquer Rhodes, which had refused him armed support against Ptolemy.

Arriving with two hundred warships, one hundred and seventy transports, forty thousand troops and thirty thousand workers, Demetrius besieges Rhodes, attempting several tactics.

The late Alexander’s marshal Ptolemy, who has occupied Egypt, declares himself king of Egypt and Libya in 304, making his capital Alexandria, where he founds a great library and museum.

Dependent, by choice, on Greeks and Macedonians in government and the army, he settles his veterans on farms throughout Egypt.

Demetrius, after a year's unsuccessful siege in which he earns the nickname Poliorcetes (“the Besieger”), and in which Ptolemy, who aids the Rhodians, is accorded the divine title Soter (Savior), concludes a peace treaty and an alliance with the island state, guaranteeing it autonomy and neutrality in his conflicts with Ptolemy.

This concession is necessary because in the meantime, …

…Cassander has invaded Attica and is besieging Athens.

Demetrius drives him out of central Greece, and the Athenians bestow on him a new religious honor, synnaos (“having the same temple”) of the temple of the goddess Athena, giving him the Parthenon as his palace.

Agathocles, who has continued to strengthen his rule over the Greek cities of Sicily, feels secure enough by about 304 to assume the title king of Sicily, and extends his influence into southern Italy and the Adriatic.

Seleucus' territorial demands (e.g., the surrender of Cilicia and the cities of Tyre and Sidon) soon rupture the previously harmonious relationship with Demetrius, who has retained control of the sea.

The possession of Syria gives him an opening to the Mediterranean, and he immediately founds, as a chief seat of government, the new city of Antioch (modern Antakya, a city in Hatay province in southern Turkey) on the banks of the Orontes River about fourteen miles (twenty-two kilometers) from the Mediterranean at the end of the fourth century CE.

He names the city in memory of his father, Antiochus, and imports colonists from Athens and Macedonia, intending it to be a western counterbalance to his eastern capital of Seleucia.

Seleucus founds the city of Europos on the Euphrates River in Syria in 303 BCE.

The new city controls the river crossing on the route between his newly founded cities of Antioch and Seleucia on the Tigris.

Seleucus embarks in 305 BCE on an expansion of his kingdom throughout the Iranian east (the upper satrapies) as far as India, intent on recovering Alexander’s Indian province.

but his advance is eventually halted by Chandragupta (Greek Sandrokottos), the founder of the Maurya dynasty of India.

In a pact concluded by the two potentates, Seleucus agrees to territorial concessions in exchange for five hundred elephants.

By this time, Chandragupta controls the Indus and Ganges plains as well as far northwestern portions of the Indian subcontinent.