The battle of Adys (or Adis) took place in late 256 BC during the First Punic War between a Carthaginian army jointly commanded by Bostar, Hamilcar and Hasdrubal and a Roman army led by Marcus Atilius Regulus. Earlier in the year, the new Roman navy had established naval superiority and used this advantage to invade the Carthaginian homeland, which roughly aligned with modern Tunisia in North Africa. After landing on the Cape Bon Peninsula and conducting a successful campaign, the fleet returned to Sicily, leaving Regulus with 15,500 men to hold the lodgement in Africa over the winter.

Instead of holding his position, Regulus advanced towards the Carthaginian capital, Carthage. The Carthaginian army established itself on a rocky hill near Adys (modern Uthina) where Regulus was besieging the town. Regulus had his forces execute a night march to launch twin dawn assaults on the Carthaginians' fortified hilltop camp. One part of this force was repulsed and pursued down the hill. The other part then charged the pursuing Carthaginians in the rear and routed them in turn. At this the Carthaginians remaining in the camp panicked and fled.

The Romans advanced to and captured Tunis, only 16 kilometres (10 mi) from Carthage. Despairing, the Carthaginians sued for peace. The terms offered by Regulus were so harsh that Carthage resolved to fight on. A few months later, at the battle of the Bagradas River (battle of Tunis), Regulus was defeated and his army all but wiped out. The war continued for a further 14 years.

The main source for almost every aspect of the First Punic War is the historian Polybius (c. 200 – c. 118 BC), a Greek sent to Rome in 167 BC as a hostage. His works include a manual on military tactics, no longer extant but he is now known for The Histories, written sometime after 146 BC, or about a century after the battle of Adys. Polybius's work is considered broadly objective and largely neutral between the Carthaginian and Roman points of view. The accuracy of Polybius's account has been much debated over the past 150 years but the modern consensus is to accept it largely at face value and the details of the war in modern sources are largely based on interpretations of Polybius's account. The historian Andrew Curry sees Polybius as being "fairly reliable"; while Dexter Hoyos describes him as "a remarkably well-informed, industrious, and insightful historian". Other, later, ancient histories of the war exist but in fragmentary or summary form and they usually cover military operations on land in more detail than those at sea. Modern historians usually take into account the later histories of Diodorus Siculus and Dio Cassius, although the classicist Adrian Goldsworthy states "Polybius' account is usually to be preferred when it differs with any of our other accounts". Other sources include inscriptions, archaeological evidence and empirical evidence from reconstructions such as the trireme Olympias.

The First Punic War between the states of Carthage and Rome began in 264 BC. Carthage was the leading maritime power in the Western Mediterranean, its navy dominating both militarily and commercially. Rome had recently unified mainland Italy south of the Arno. The immediate cause of the war was a wish to control the Sicilian town of Messana (modern Messina). More broadly both sides wished to control Syracuse, the most powerful city-state in Sicily. By 260 BC the war had grown into a struggle in which the Romans wanted at least control the whole of Sicily.

The Carthaginians were engaging in their traditional policy of waiting for their opponents to wear themselves out, in the expectation of then regaining some or all of their possessions and negotiating a mutually satisfactory peace treaty. The Romans were essentially a land-based power and had gained control of most of Sicily using their army. The war there had reached a stalemate, as the Carthaginians focused on defending their well-fortified towns and cities; these were mostly on the coast and so could be supplied and reinforced by sea without the Romans being able to use their superior army to interfere. The focus of the war shifted to the sea, where the Romans had little experience; on the few occasions they had previously felt the need for a naval presence they had relied on small squadrons provided by their allies. In 260 BC Romans set out to construct a fleet using a shipwrecked Carthaginian quinquereme as a blueprint for their own ships.

Naval victories at Mylae and Sulci, and their frustration at the continuing stalemate in Sicily, led the Romans to focus on a sea-based strategy and to develop a plan to invade the Carthaginian heartland in North Africa and threaten their capital, Carthage (close to what is now Tunis). Both sides were determined to establish naval supremacy and invested large amounts of money and manpower in increasing and maintaining the size of their navies.

The Roman fleet of 330 warships plus an unknown number of transport ships sailed from Ostia, the port of Rome, in early 256 BC, commanded by the consuls for the year, Marcus Atilius Regulus and Lucius Manlius Vulso Longus. They embarked approximately 26,000 picked legionaries from the Roman forces on Sicily. The Carthaginians were aware of the Romans' intentions and mustered all 350 available warships under Hanno and Hamilcar, off the south coast of Sicily to intercept them. A combined total of about 680 warships carrying up to 290,000 crew and marines met in the battle of Cape Ecnomus. The Carthaginians took the initiative, anticipating that their superior ship-handling skills would tell. After a prolonged and confused day of fighting the Carthaginians were defeated, losing 30 ships sunk and 64 captured to Roman losses of 24 ships sunk.