by her ancient rivals for the "harsh treatment of her subjects" as well as for "greed and cruelty". Her Libyan Berber sharecroppers, for example, were required to pay half of their crops as tribute to the city-state during the emergency of the First Punic War. The normal exaction taken by Carthage was likely "an extremely burdensome" one-quarter. Carthage once famously attempted to reduce the number of its Libyan and foreign soldiers, leading to the Mercenary War (240–237 BC). The city-state also seemed to reward those leaders known to deal ruthlessly with its subject peoples, hence the frequent Berber insurrections. Moderns fault Carthage for failure "to bind her subjects to herself, as Rome did [her Italians]", yet Rome and the Italians held far more in common perhaps than did Carthage and the Berbers. Nonetheless, a modern criticism is that the Carthaginians "did themselves a disservice" by failing to promote the common, shared quality of "life in a properly organized city" that inspires loyalty, particularly with regard to the Berbers. Again, the tribute demanded by Carthage was onerous. [T]he most ruinous tribute was imposed and exacted with unsparing rigour from the subject native states, and no slight one either from the cognate Phoenician states. [...] Hence arose that universal disaffection, or rather that deadly hatred, on the part of her foreign subjects, and even of the Phoenician dependencies, toward Carthage, on which every invader of Africa could safely count as his surest support. [...] This was the fundamental, the ineradicable weakness of the Carthaginian Empire [....] The Punic relationship with the majority Berbers continued throughout the life of Carthage. The unequal development of material culture and social organization perhaps fated the relationship to be an uneasy one. A long-term cause of Punic instability, there was no melding of the peoples. It remained a source of stress and a point of weakness for Carthage. Yet there were degrees of convergence on several particulars, discoveries of mutual advantage, occasions of friendship, and family. The Berbers gain historicity gradually during the Roman era. Byzantine authors mention the (Amazigh) as tribal people raiding the monasteries of Cyrenaica. Garamantia was a notable Berber kingdom that flourished in the Fezzan area of modern-day Libya in the Sahara desert between 400 BC and 600 AD. Roman-era Cyrenaica became a center of early Christianity. Some pre-Islamic Berbers were Christians (there is a strong correlation between adherence to the Donatist doctrine