The Siege of Himera was the second major battle of the First Syracusan War the ending stage of the Syracusan Advance. After a crushing victory at Capilium, the Himeran armies were constantly on the run from the victorious Syracusan Armies, who eventually pursued the fleeing army to the capital city of Himera. Because of an extensive fortification system, as well as the sheer immense size of the city, Alextrus was unable to directly assault the city and instead was forced to wait out the Himeran defenders. To Alextrus, this action might cost him the war, as his second army, composed now of 5000 men, were barely managing to slow down the Athenian advance towards Himera. However, The cold winter forced the Athenian Army to grind to a halt for several months, and gave Alextrus the upper hand. When word reached the Athenian General, Tisinyus, that the city was near to surrender, he ordered 1000 of his troops to rush past the Syracusan second army and reinforce the city.
As a result of bad communication, Himera believed the Athenians had abandoned their oath to assist them, and prepared themselves to surrender. Many of the military commanders fled the city through secret tunnels, unaware of the reinforcement army. Finally, the Athenian reinforcements arrived in mid-February, and camped behind the Syracuse army. Alextrus, under orders from Syracuse to execute the assault, attacked the walls with half his force, while striking the Athenian's in a night attack. The Athenians were able to re-form slightly, marching into phalanx formation, but quickly became encircled. The expedition force was decimated, with no record of Athenian survivors.
With the Athenians defeated, Alextrus pulled the other half of the army, and completed his assault. After about a day of intense fighting, the attacking force broke the Himerans center, and the battle quickly became a mess of chaotic disaster for the Himeran forces. Alextrus marched into the city a few hours later, and declared Himera's Oligarchy disbanded. Later that evening, it is said that the Syracusan Army feasted on lavish foods and wines, celebrating their second decisive victory.