In this era, the predominant "warfare" consisted of chronic small-scale raiding and cattle-rustling against other clans and, later, neighbouring hill-tribes such as the Sabini and Aequi. Only occasionally did the clan war-bands join together to form a larger force, in order to face a major threat from neighbouring tribes. It is likely that the heroic tales in Livy's first three books derive from old ballads celebrating such raids, orally transmitted through the generations within aristocratic clans. At this time, it is likely that Roman warriors, both foot and mounted, were unarmoured, carrying only light shields and leather helmets. It appears that the "Early Roman army" in the sense of an organised national force with standard equipment did not become established before the period 600-500 BC, when both the ancient chroniclers and archaeology indicate major changes in organisation and equipment. The critical changes were the adoption by the infantry of Greek-style hoplite equipment, most likely borrowed from the Greek colonies of southern Italy (Magna Graecia), featuring metal body-armour; and the concomitant differentiation of the section of the citizen-body who were wealthy enough to pay for such equipment (known as the "classis", or "class") from those who were not and continued to serve as unarmoured light infantry ("infra classem", or "beneath the class"). According to Livy, Romulus (traditional reign dates: 753–717 BC) raised ten "centuriae" (military units of 100 men) of infantry from each of the three original "tribes" of Rome which he had founded - the "Ramnes", "Tities" and "Luceres". (Although the Latin term "tribus" - literally "in three parts" - is conventionally translated as "tribe", the term "constituency" would be more precise, as they were artificial divisions for administrative purposes. The Romans always used the terms "gentes" or "nationes" to mean "tribes" in the sense of ethnic groups). But the establishment of these "centuriae" (and even of the tribes themselves) is probably anachronistic, and in reality dates from much later in the regal era, probably in the period 600-550 BC. The initial 30 "centuriae" were then doubled to 60 in the period around 550 BC, according to the scholar P. Fraccaro's interpretation of the so-called Servian centuriate organisation.