Isernia (Latin: Aesernia or, in Pliny and later writers, Eserninus, or in the Antonine Itinerary, Serni;) is a town and comune in the central Italian region of Molise, and the capital of Isernia province. Isernia is a flourishing center of pasta makers, stone masons, and embroidery crafts.

Situated on a rocky crest rising from 350 m to 475 m between the Carpino and the Sordo rivers, the plan of Isernia still reflects the ancient layout of the Roman town, with a central wide street, the cardo maximus, still represented by Corso Marcelli, and side streets at right angles on both sides.

he commune of Isernia includes 16 frazioni. The most densely populated is Castelromano which is positioned in a plain at the base of the La Romana mount (862 m), 5 km far from Isernia.

The area of Isernia was settled at least 700,000 years ago: the nearby site called Pineta has been cited in the magazine Science as the most ancient site where traces of use of fire by men have been found.
The city's Roman name, Aesernia, reflects probably a former Samnite toponym, but a connection to an Indo-European root, aeser, which means "water", is tenuous.

Classical Aesernia was a city of Samnium, included within the territory of the Pentri tribe, situated in the valley of the Vulturnus (modern Volturno), on a small stream flowing into that river, and distant 22 km from Venafrum (modern Venafro). The Itinerary (in which the name is written "Serni") places it on the road from Aufidena to Bovianum, at the distance of 28 M.P. from the former, and 18 from the latter; but the former number is corrupt, as are the distances in the Tabula Peutingeriana. (Itin. Ant. p. 102; Tab. Peut.; Plin. iii. 12. 17; Ptol. iii. 1. § 67; Sil. Ital. viii. 568.)

The first mention of it in history occurs in 295 BCE, at which time it had already fallen into the hands of the Romans, together with the whole valley of the Vulturnus. (Livy x. 31.) After the complete subjugation of the Samnites, a colony, with Latin rights (colonia Latina) was settled there by the Romans in 264 BCE the city, a key communication center between southern Italy and the inner Appennine Regions. This colony is again mentioned in 209 BCE as one of the eighteen which remained faithful to Rome at the most trying period of the Second Punic War. (Liv. Epit. xvi. xxvii. 10; Vell. Pat. i. 14.) During the Social War it adhered to the Roman cause, and was gallantly defended against the Samnite general Vettius Cato, by Marcus Claudius Marcellus, nor was it till after a long protracted siege that it was compelled by famine to surrender, 90 BCE. Henceforth it continued in the hands of the confederates; and at a later period of the contest afforded a shelter to the Samnite leader, Papius Mutilus, after his defeat by Lucius Cornelius Sulla. It even became for a time, after the successive fall of Corfinium (modern (Corfinio) and Bovianum, the headquarters of the Italic League. (Liv. Epit. lxxii, lxxiii.; Appian B.C. i. 41, 51; Diod. xxxvii. Exc. Phot. p. 539; Sisenna ap. Nonium, p. 70.) At this time it was evidently a place of importance and a strong fortress, but it was so severely punished for its defection by Sulla after the final defeat of the Samnites in 84 BCE, that Strabo speaks of it as in his time utterly deserted. (Strab. v. p. 238, 250.)

We learn, however, that a colony was sent there by Julius Caesar, and again by Augustus; but apparently with little success, on which account it was recolonized under Nero. It never, however, enjoyed the rank of a colony, but appears from inscriptions to have been a municipal town of some importance in the time of Trajan and the Antonines. To this period belong the remains of an aqueduct and a fine Roman bridge, still visible; while the lower parts of the modern walls present considerable portions of polygonal construction, which may be assigned either to the ancient Samnite city, or to the first Roman colony. The modern city is still the see of a bishop. (Lib. Colon. pp. 233, 260; Zumpt, de Coloniis, pp. 307, 360, 392; Inscrr. ap. Romanelli, vol. ii. pp. 470, 471; Craven's Abruzzi, vol. ii. p. 83; Hoare's Classical Tour, vol. i. p. 227.) The massively constructed podium now unlying the cathedral probably supported the Capitolium.

Even after the fall of the Roman Empire, Isernia has suffered destruction numerous times in history. Isernia was destroyed by the Saracens in 800, sacked by Markward of Anweiler, Count of Molise, in 1199, and set on fire in 1223 by the soldiers of Frederick II. In 1519 it was freed from feudal servitude by Charles V, Holy Roman Emperor and became a free city.

Earthquakes in 847, 1349, 1456 and 1805 caused massive destruction.
On the morning of September 10, 1943, during World War II, American planes launched their bombs from B-17 Flying Fortress planes over a crowded town on market day causing thousands of deaths.[citation needed] In the following weeks they came back twelve times without ever hitting their targets: the bridges of Isernia, Cardarelli and Santo Spirito, then built entirely of iron, towards the internal area. All the bridges were vital to the German retreat.

In 1970 Isernia became the capital of the homonymous province, created out of part of the province of Campobasso.

The coins of Aesernia, which are found only in copper, and have the legend "AISERNINO", belong to the period of the first Roman colony; the style of their execution attests the influence of the neighboring Campania. (Millingen, Numismatique de l'Italie, p. 218.)

Main sights
Although having been object of repeated destruction, Isernia preserves a large number of monuments of fairly good archaeological interest. The historical center still keeps intact the spare map structure of the Roman cities: in fact it represents the largest raced Marcelli street, around which there is an infinity of alleys and little spares, as for example, "Trento e Trieste" spares. The famous Fraterna Fountain is the main symbol in this town and it was built in the 13th century : it is made up of living- stone's slabs coming from ruined Roman monuments, while all the rest is a work of local masters, as it was built by the Rampini family in Isernia.

La Pineta
Isernia is also known for the archaeological excavation located within its borders, at Isernia La Pineta. Isernia La Pineta contains thousands of bones and stone tools covering 24,000 square yards. It was discovered in 1979, by an amateur naturalist noticed a bone sticking out of the side of a cut that had been created by the construction of the Napoli-Vasto motorway. The site was clearly created by humans, but its purpose is still unknown. The man who lived there was called Homo Aeserniensis.