To Tacitus, who wrote a biography of his father-in-law, the Roman governor of Britain from AD77 to 84, Agricola, the whole of Britain north of the Forth-Clyde isthmus was “Caledonia”. However, Tacitus never calls the inhabitants of the country Caledonians, only “Britons”. The geographer Ptolemy, writing in the mid-2nd century (but apparently using data gleaned around the time of Agricola), lists the Caledonians (Caledonii) as just one of several tribes living beyond the isthmus. So, although the whole country was called Caledonia, the Caledonians were but one tribe inhabiting that country. (See: British Tribes: Caledonia.)
Dio Cassius, discussing events in northern Britain during the period 197–211, notes:
“There are two principal races of the Britons, the Caledonians and the Maeatae, and the names of the others have been merged in these two. The Maeatae live next to the cross-wall which cuts the island in half, and the Caledonians are beyond them.”
Dio Cassius (Xiphilinus) ‘Romaika’ Epitome of Book LXXVI Chapter 12
It is generally believed that Dio's “cross-wall” is the Antonine Wall (on the Forth-Clyde line), in which case, the tribes of Caledonia had amalgamated to produce two major groups: the Maeatae, to the immediate north of the Wall, and to the north of them the Caledonians. (See: The Caledonian Campaigns of Septimius Severus.)
Almost a century later, in a panegyric delivered in 297, appears the earliest extant mention of the Picts (Picti). The anonymous author makes a poetic reference to Julius Caesar having had a relatively easy task invading Britain, since his opponents were:
“... primitive and used only to foes as yet half-naked, like the Picts and the Irish [Hiberni] ...”
‘Panegyrici Latini’: ‘VIII. Panegyric on Constantius Caesar’ Chapter 11
A little later, in 310, another panegyric, also anonymous, refers to:
“... the forests and marshes of the Caledonians [Caledones] and other Picts ...”*
‘Panegyrici Latini’: ‘VI. Panegyric on Constantine’ Chapter 7
The so-called ‘Verona List’, of c.314, names the Scots, the Picts and the Caledonians amongst the “barbarian tribes who have increased under the emperors”. This is the final historical reference to the Caledonians, and also the first reference to the Scots (Scoti or Scotti).
Ammianus Marcellinus, writing about the, so-called, Barbarian Conspiracy of 367, says:
“... at that time the Picts, divided into two tribes, called Dicalydones and Verturiones, as well as the Attacotti, a warlike race of men, and the Scots, were ranging widely and causing great devastation ...”
Ammianus Marcellinus ‘Res Gestae’ Book XXVII Chapter 8
Presumably the Caledonians (Caledonii/Caledones) had evolved into the Dicalydones – the similarity of name is clear – and the Maeatae had metamorphosed into the Verturiones. It would seem then that, by the early-4th century, all the tribes beyond the Forth-Clyde line had come to be known, collectively, as Picti by the Romans. Scotti also seems to be a new name for an old foe – in this instance Irish raiders. The ‘Panegyric on Constantius Caesar’ of 297 linked the Picts with the Hiberni, but thereafter they are always linked with the Scotti. The poet Claudian (Claudius Claudianus), writing in 398, confirms that the Scots are indeed Irish:
“... ice-bound Hibernia [Ireland] wept for the heaps of slain Scots.”
Claudian ‘Panegyricus de Quarto Consulatu Honorii’ (Panegyric on the Fourth Consulship of Honorius)
Often, Scotti is said to be derived from a Goidelic word, and mean ‘pirate’ or ‘raider’, but this is speculation only. According to one legend the Scots were named from, Pharaoh's daughter, Scota – wife of the man who led their forebears from Egypt at the time of Moses.
The origins of the name Pict has been much debated (along with many other aspects of the Picts, who thrived for over five hundred years but about whom remarkably little is known). What they called themselves is not known – the Picts left no literature – but the Latin word Picti would appear to mean ‘painted people’ (pictus = ‘painted’, hence the English word ‘picture’). In 208, Septimius Severus arrived in Britain to campaign against the tribes of Caledonia (the Maeatae and the Caledonians). Herodian, a contemporary of Severus, writes:
A, late-16th century, vision of a Pictish warrior (clearly based on Herodian's description of the “barbarians” of Caledonia) by John White. The overall blue tinting of the body is inspired by a remark made by Julius Caesar, who had spent a few weeks in the south-eastern corner of Britain in 55BC and 54BC: “All the Britons, without exception, stain themselves with woad, which produces a blueish tint; and this gives them a wild look in battle.”
“Most of the regions of [northern] Britain are marshy, since they are flooded continually by the tides of the ocean; the barbarians are accustomed to swimming or wading through these waist-deep marsh pools; since they go about naked, they are unconcerned about muddying their bodies. Strangers to clothing, they wear ornaments of iron at their waists and throats; considering iron a symbol of wealth, they value this metal as other barbarians value gold. They tattoo their bodies with coloured designs and drawings of all kinds of animals; for this reason they do not wear clothes, which would conceal the decorations on their bodies. Extremely savage and warlike, they are armed only with a spear and a narrow shield, plus a sword that hangs suspended by a belt from their otherwise naked bodies. They do not use breastplates or helmets, considering them encumbrances in crossing the marshes.”
Herodian ‘History of the Empire after Marcus’ Book III Chapter 14
Almost a century after Severus, the name Pict appeared (297). Another century later, in 400, the poet Claudian talked of Britain (in female personification) being:
“... clothed in the skin of some Caledonian beast, her cheeks tattooed, and an azure cloak, rivalling the swell of Ocean, sweeping to her feet ...”
Claudian ‘De Consulatu Stilichonis’ (On the Consulship of Stilicho) Book II
And, in 402, of:
“... the strange devices tattooed on dying Picts.”
Claudian ‘De Bello Gothico’ (On the Gothic War)
And he had, in 396, referred to:
“... the well-named Picts ...”
Claudian ‘Panegyricus de Tertio Consulatu Honorii’ (Panegyric on the Third Consulship of Honorius)
Possibly, then, it was their tendency to decorate themselves with extravagant body-art that caused the Romans to nickname them Picti: ‘painted people’. On the other hand, maybe the association of tattooing with British “barbarians” was based not on reality, but on a stereotyped notion of those distant savages. In other words, perhaps it was a myth that the Picts tattooed their bodies. The British cleric Gildas, writing in about 545(?), who refers to the Picts and the Scots as “dark swarms of worms”, and says of them:
“Differing partly in their habits, yet alike in one and the same thirst for bloodshed – in a preference also for covering their villainous faces with hair rather than their nakedness of body with decent clothing ...”
Gildas ‘De Excidio Britanniae’ Chapter 19
It is difficult to believe that Gildas would have passed-up the opportunity to make disparaging remarks about tattoos if the Picts were particularly noted for them. Perhaps Picti was simply a Latinization of their native name (which could have had a completely different meaning). Nevertheless, in the early-600s, the Spanish bishop and encyclopaedist, Isidore of Seville wrote:
“It is not simply in clothing but in physical appearance also that some groups of people lay claim to features peculiar to themselves as marks to distinguish them, so that we see the curls [perhaps topknot] of the Germans, the mustaches and goatees of the Goths, the tattoos of the Britons. The Jews circumcise the foreskin, the Arabs pierce their ears, the Getae with their uncovered heads are blond, the Albanians shine with their white hair. The Moors have bodies black as night, while the skin of the Gauls is white. Without their horses, the Alans are idle. Nor should we omit the Picts, whose name is taken from their bodies, because an artisan, with the tiny point of a pin and the juice squeezed from a native plant, tricks them out with scars to serve as identifying marks, and their nobility are distinguished by their tattooed limbs.”*
Isidore of Seville ‘Etymologiae’ (or ‘Origines’) Book XIX Part 23 No. 7
The image of the highly-decorated, naked, Pict still seems to be stuck in the public imagination. Whatever its derivation, it is apparent that Picti was a new collective name for the disparate tribes already living beyond the Forth-Clyde isthmus. According to the mythology that developed, however, the Picts were a migrant race of people who eventually settled in Britain. In the 8th century, the Anglo-Saxon monk and historian, Bede, wrote:
“... at first this island had no other inhabitants but the Britons, from whom it derived its name, and who, coming over into Britain, as is reported, from Armorica, possessed themselves of the southern parts thereof. Starting from the south, they had occupied the greater part of the island, when it happened, that the nation of the Picts, putting to sea from Scythia, as is reported, in a few ships of war, and being driven by the winds beyond the bounds of Britain, came to Ireland and landed on its northern shores. There, finding the nation of the Scots, they begged to be allowed to settle among them ... The Scots answered that the island could not contain them both; but “We can give you good counsel,” said they, “whereby you may know what to do; we know there is another island, not far from ours, to the eastward, which we often see at a distance, when the days are clear. If you will go thither, you can obtain settlements; or, if any should oppose you, we will help you.” The Picts, accordingly, sailing over into Britain, began to inhabit the northern parts thereof, for the Britons had possessed themselves of the southern. Now the Picts had no wives, and asked them of the Scots; who would not consent to grant them upon any other terms, than that when any question should arise, they should choose a king from the female royal race rather than from the male: which custom, as is well known, has been observed among the Picts to this day.”
Bede ‘Historia Ecclesiastica’ Book I Chapter 1
The Birth of Nations: Scotland    
Claudian by Maurice Platnauer
‘Panegyrici Latini’ by Stanley Ireland
Dio Cassius ‘Romaika’ by Earnest Cary
Gildas ‘De Excidio Britanniae’ by Hugh Williams
Ammianus Marcellinus ‘Res Gestae’ by John C. Rolfe
Bede ‘Historia Ecclesiastica Gentis Anglorum’ by A.M. Sellar
Julius Caesar ‘Commentarii de Bello Gallico’ by T. Rice Holmes
Herodian ‘History of the Empire after Marcus’ by Edward C. Echols
Isidore of Seville ‘Etymologiae’ by S.A. Barney, W.J. Lewis, J.A. Beach & O. Berghof
Traditionally, the ‘Panegyric on Constantius Caesar’ is attributed to Eumenius. However, Nixon and Rodgers (‘In Praise of Later Roman Emperors’, 1994) convincingly reject this attribution.
Constantius Chlorus: western Caesar 293–305, western Augustus 305–306. (See: New Empires.)
Marjorie O. Anderson, in ‘Kings and Kingship in Early Scotland’ (Revised Edition, 1980), writes: “This is the only reading for which there is manuscript authority. The often-cited “alternative reading” ... “Caledones, Picts and others”, seems to have originated as a quite unnecessary emendation by Franz Eyssenhardt in 1867. It was adopted in the edition by Emil Baehrens (father of W. Baehrens) in 1874, which was unfortunately followed by Holder in his article Picti [1904] ... Holder's influence still perpetuates the idea that Caledones and Picti were the names of two distinct though related peoples.”
The Attacotti (various spellings) are a mysterious people who flit through history at this time. In a famous and much discussed passage, St Jerome (Hieronymus, c.347–419/20) apparently accuses the Attacotti of cannibalism: “... I myself, a youth on a visit to Gaul, heard that the Atticoti, a British tribe, eat human flesh, and that although they find herds of swine, and droves of large or small cattle in the woods, it is their custom to cut off the buttocks of the shepherds and the breasts of their women, and to regard them as the greatest delicacies.” (‘Against Jovinianus’ Book II Chapter 7.)  It is suspected that the Attacotti came either from Ireland (despite Jerome, who calls them “a British tribe”) or the Western Isles.
Earlier in the ‘Etymologiae’ (Book IX 2.103), Isidore apparently slips-up, stating: “The Scots in their own language receive their name from their painted bodies, because they are marked by tattoos of various figures made with iron pricks and black pigment.”   Presumably Isidore meant to say the Picts rather than the Scots – indeed, as quoted in the ‘Pictish Chronicle’ (as it is sometimes called, see: The Poppleton Manuscript), Isidore's “Scots” is amended to “Picts”.
Isidore had apparently started work on the ‘Etymologiae’ before 621, but it was still unfinished at the time of his death in 636.
‘Commentarii de Bello Gallico’ (The Gallic War) Book V Chapter 14.
See: Caesar's Expeditions.