Seleucus, returning his attention to his former province, Babylonia, in August 312 is able to reconquer Babylon with only a small army.

This conquest marks the beginning of the Seleucid era, which is dated Dios 1 (Oct. 7), 312, in the Macedonian calendar and Nisan 1 (April 3), 311, in the Babylonian calendar.

He establishes his imperial capital at Seleukeia on the Tigris, located just south of present Baghdad.

Ptolemy launches an invasion of southern Syria while Antigonus is engaged in the conquest of Caria, arriving in Gaza in early 312 BCE with Seleucus at the head of eighteen thousand infantry and four thousand cavalry.

Demetrius decides to offer battle, but is routed in the Battle of Gaza, in which the Egyptian contingents are decisive; losing five hundred men killed, a further eight thousand taken prisoner, and losing all his elephants.

He retreats to Tripolis in Phoenicia.

The Illyrian king Glaucias, operating to the northwest of the Macedonian kingdom seizes Durrës in 312 and expels the Greeks.

Rome constructs its first aqueduct, the Aqua Appia, in 312.

Only about 0.7 feet (0.2 meters) of its total ten-mile (sixteen-kilometer) length runs aboveground; most of the rest is simply a stone-lined ditch.

Construction begins on the Via Appia (Appian Way) in 312 across the malarial and unhealthful Pontine Marshes in south central Italy, representing the first attempt at artificially draining the region, barred by sand dunes from natural drainage into the Tyrrhenian Sea and bordered on the west by the Albani Hills and the Lepini Mountains.

Built at the instigation of Appius Claudius Caecus, who pays for part of the work himself, the Via Appia—constructed of stones, rubble, and concrete—is laid on an alternative route from Rome to …

…Capua, a city recently crushed in the Samnite War.

When complete, the Via Appia will ensure communications even in the rainy season.

Cassino, a town of the Volsci people in Frosinone province in the Lazio region of central Italy, situated on the Rapido River southeast of Rome, comes under Roman control in 312.

The coalition has from 315 BCE to 311 BCE fought indecisively against Antigonus, who has shown himself energetic, resourceful, and imaginative, but unable to strike a decisive blow.

In view of this new threat from the East, Antigonus decides to make peace with all of his adversaries except Seleucus.

He orders Nicanor, one of his generals, to invade Babylonia from the east and his son Demetrius to attack it from the west, but they fail to oust Seleucus.

Agathocles invades the last Carthaginian holdings on Sicily in 311 BCE, thereby breaking the terms of the current peace treaty, and lays siege to Akragas.

Military success had seemed to flow with the Samnites until 314 BCE.

Campania is on the verge of deserting Rome.

Peace is established between Rome and some Samnite towns.

The tide of the war turns in 311, when the Samnites are joined by Etruscan cities that have decided to join a showdown against Roman power.

However, the Samnites are unable to prevent the Romans from establishing fortified colonies around the edges of the Samnite state; these serve as bases for attack.

Agathocles saves himself from certain disaster in 310 BCE by breaking through the blockade and attacking his enemy's homelands in Africa with considerable success.