Circa 200–15 BC: Many “native” tribes (mostly Celtic) in this region were on the move and/or in gradual and erratic decline. Various Germanic tribes made major and minor incursions from the north and east during this period, and Roman military expeditions made minor incursions from the south starting around 100 BC.

15 BC: Tiberius (Tiberius Claudius Nero; who later became Roman Emperor) and his legions (under Emperor Augustus [Gaius Octavius Thurinus, Octavian, Gaius Julius Caesar] moved east through the Rhodanus (Rhone) and Rhenus (Rhine) valleys; conquered the Helvetti (Celtic), Rhaeti (Retti, Rhaetians; Celtic-Etruscan?), and other tribes (mostly Celtic); and established the original Roman province of Rhaetia (present Switzerland and southwestern Germany).

That same year, Tiberius’ younger brother, Drusus (Nero Claudius Drusus Germanicus or Drusus Senior), and his legions (under Emperor Augustus) moved north through the Brenner/Brennero, Rheschen/Resia, and other natural Alpine passes; conquered the Vindelici (Vindelicii) and other tribes (mostly Celtic); and established the original Roman province of Vindelicia (present northern Italy, Austrian Tyrol, and southeastern and south-central Germany).

15 BC–45 AD: Romans quickly settled Rhaetia and Vindelicia. Legio XXI Rapax (Predator) was based in Rhaetia from about 15 BC to 9 BC, and Legio XIII Gemina (Twin) was based there from about 9 BC until about 45 AD. The Danube River formed a natural northern border/barrier for most of both provinces.

Circa 15 BC–Circa 95 AD: Rhaetia was administered by a military Prefect. Cambodunum [present Kempten im Allgäu, Germany] may have been Rhaetia’s first capital.

1st–2nd centuries AD (General): Romans outnumbered, intermarried with, and “Romanized” the remaining local (mostly Celtic) populations. Rhaetian/ Vindelician communities, economy, and quality of life improved. Their populations became mostly Celtic-Roman. Germanic people from Germania often traveled to Rhaetia/Vindelicia to trade, and occasionally (less often than in earlier and later centuries) to immigrate, raid, or invade the region. Only one Roman legion was based in Rhaetia/Vindelicia at any given time, until about 45 AD and again after about 165 AD. Other legions, vexillationes, auxiliaries, and local militias temporarily operated in Rhaetia/Vindelicia and adjacent Germania.

Circa 40 AD: Romans built the first Rhaetian "Limes" (wall, limites) along the Danube River south bank, mostly of earth and wood palisades.

Circa 50 AD: Via Claudia Augusta, the first Roman road to connect Rhaetia/Vindelicia with Italia, was completed. It was the most important route between Rhaetia and Italia until about 200. Via Claudia Augusta extended from Altinum (present Altino, Italy) on its southeast end and Hostilia (present Ostiglia, Italy) on its south end, to Summuntorium (present Burghöfe bei Mertingen/Burghöfe an die Donau, near Donauwörth, Germany) on its north end. From south to north, it passed through Tridentum (present Trient/Trento, Italy) – Castrum Maiense (present Meran/Merano, Italy) – Pons Drusi (later, Bauzanum and present Bozen/Bolzano, Italy) – present Resia Pass (Reschenpass/Passo Resia), Italy/Austria – present Landeck and Imst, Austria – Foetibus (present Füssen, Germany) – Augusta Vindelicorum (present Augsburg, Germany).

69: Romans defeated Helvetti revolt.

Circa 74–100: Rhaetia was expanded by conquering, settling, and adding the Agri Decumates (Decumates Fields; present southwestern Germany). Romans built major roads between Rhaetia/Vindelicia and Germania Superior to the west, and Noricum to the east, as well as major and minor internal roads within Rhaetia/Vindelicia.

Circa 90–100: Rhaetia was further expanded by adding Vindelicia. Romans built the second Rhaetian “Limes” (Vallum Hadriani; earth ditches and walls with wood palisades) along the new, more northerly border with “Germania” (between present Lorch, Germany and Roman “Abusina” [present Eining, Germany]). The new, larger province of Rhaetia was administered by a Governor (Procurator) of equestrian rank, based in Augusta Vindelicorum (present Augsburg), which became Rhaetia’s capital until the end of Roman rule in Rhaetia.

Circa 140-160: Romans strengthened the Rhaetian Limes by replacing the earth and wood palisade walls with stone walls.

165–180: Emperor Marcus Aurelius (Caesar Marcus Aurelius Antoninus Augustus) founded Legio III Italica Concors in northern Italy during 165, for the Marcomannic Wars (165–175 and 177–182) in Germania, Rhaetia, and Noricum. Legio III Italica operated throughout Rhaetia and adjacent Germania. They also built Castra Regina (present Regensburg, Germany; on the Danube River’s northernmost point) in 171–179.

(Legio III Italica was based in Castra Regina until the end of the 4th century [per archeological evidence] or early 5th century [per Notitia Dignitatum, circa 420]. Over almost four centuries, Legio III Italica vexillationes guarded the Rhaetian Limes, Danubian crossings, and Alpine passes; prevented and responded to raids and invasions in and around Rhaetia, supported several successful contenders for the Emperor’s throne; and vexillationes also served in military operations elsewhere throughout the Empire.)

Circa 182: Emperor Commodus (Marcus Aurelius Commodus Antoninus, originally Lucius Aelius Aurelius Commodus) settled (bought) peace with the Marcommani.

Circa 180–294: Rhaetia was administered by a Governor who was the Commander of Legio III Italica and also a Senator of Praetorian rank (Legatus Augusti per Praetore).

3rd–5th centuries (General): The Western Roman Empire (including Rhaetia) was increasingly raided, invaded, and settled by Germanic and Eastern tribes. Rhaetian communities, economy, and quality of life declined. Christianity became more widespread in Rhaetia, with Bishop’s seats in Augusta Vindelicorum and Castra Regina.

3rd century: Rhaetia’s population was increasingly Germanic, became Celtic-Germanic-Roman.

Circa 200: A newer, second Roman road became the most important route between Rhaetia and Italia. It connected Pons Drusi (present Bozen/Bolzano) and Augusta Vindelicorum (present Augsburg), which where already connected by the longer middle segment of Via Claudia Augusta, but it used a shorter and lower route through Brenner Pass/Passo de Brennero.

200–201: Marcomanni attack the Rhaetian “Agri Decumates”.

213: Roman forces under Emperor Caracalla (Marcus Aurelius Antoninus) attacked and defeated Germanic forces in Germania.

233–235: Roman forces under Emperor Alexander Severus (Marcus Aurelius Severus Alexandrus), and later under Emperor Maximinus Thrax (Caius Julius Verus Maximinus, Maximinus the Thracian, or Maximinus I) defeated Germanic forces in Gaul, Upper Germany, and Rhaetia. However, most Rhaetian communities, infrastructure, and economy suffered setbacks that lasted for decades. Germanic forces sacked Castra Regina (present Regensburg) and Abusina (present Eining, Germany).

254-258: Germanic forces were generally victorious, as the Alamanni (Alemanni) destroyed Roman forts and communities in Rhaetia, Germania Superior and Inferior; and raided much of Gaul, Hispania, and Italia. They again sacked Castra Regina.

259–260: Although Roman forces under Emperor Gallienus (Publius Licinius Egnatius Gallienus) defeated Germanic forces near Mediolanum (present Milan, Italy), the Romans permanently lost the Rhaetian “Agri Decumates”. Germanic forces again sacked and Abusina.

The Alamanni quickly settled in that large area, which projected into Rome’s new northern border, provided a bypass for the Rhine and Danube Rivers, and made it easier for the Alamanni to threaten Gaul, Rhaetia, and Italia.

Late 3rd century: Germanic forces again sacked Castra Regina (present Regensburg).

Circa 294–305: Emperor Diocletian (Gaius Aurelius Valerius Diocletianus, born Diocles) made Rhaetia part of the Italy Diocese and divided Rhaetia into two sub-provinces: Raetia Prima in the south (former Rhaetia, with its capital in Curia Rhaetorium [present Chur, Switzerland]); and Raetia Secunda in the north (former Vindelicia, with its capital in Augusta Vindelicorum). Rhaetia was ruled by a Dux, and Raetia Prima (Curiensis) and Raetia Secunda (Vindelica) were each administered by a Praeses (low-ranking Governor).

Legio III Italica (based in Castra Regina) was divided into six vexillationes, which increasingly took part in military operations outside Rhaetia during the 4th century, and thereby weakened Roman defenses in Rhaetia.

4th century: The Celtic–Germanic–Roman civilian population in the “vicus” around Castra Regina’s walls gradually moved inside the castel’s defensive walls. Castra Regina gradually lost its military function and character.

Late 4th or Early 5th century: The last Legio III Italica vexillation left Castra Regina (present Regensburg) to the local Celtic–Germanic–Roman civilian population, by then housed mostly within the castel–city’s deteriorating defensive walls.

401: The Vandals (Germanic) and Alans (Iranian-Sarmatian) fled from the Huns, invaded Rhaetia and Noricum. Roman Magister Militum (high-ranking general) Stilicho (Flavius Stilicho; of Vandal father and Roman mother) and his barbarized Roman legions defeated them, then placed them as “Foederati” in northern Italia.

Circa 401: Romans withdrew from the Rhaetian Limes.

Circa 450–453: The Huns and their Germanic and other allies (under Attila the Hun) invaded Gaul, Rhaetia, and Italia. Among many other Roman communities, they sacked Rhaetia’s capital Augusta Vindelicorum (present Augsburg).

5th–6th centuries: Raetia Secunda: The Alamanni, Bohemians, Franks, Juthungians, Elbians, Marcomanni, Danubuan Suebians, Skirians, Rugians, Thuringians, Lombards, Visigoths, Ostrogoths, and other Germanic and Eastern tribes invaded and settled in Raetia Secunda during the “Migration Period” (Völkerwanderung). They outnumbered the remaining Celtic-Roman population, and temporarily broke connections with Italy. The Celtic-Roman culture and language was replaced by Germanic culture and language/dialects. Christianity was replaced by Germanic paganism, except around Augsburg for several centuries. Raetia Secunda became part of the Duchy of Bavaria, and “Rega-nespurc” (former Castra Regina and future Regensburg) became Bavaria’s first capital.

Rhaetia Prima: The same Germanic and Eastern tribes also invaded and settled in much of Rhaetia Prima during this same period, but too a lesser extent than in Raetia Secunda. Many connections to Italy continued. Christianity and the Rhaetian – Romanche – Ladin languages survived in southeastern Switzerland and northern Italy.

Important Roman Rhaetian cities were: Augusta Vindelicorum (Augsburg), Castra Regina (Regensburg), Cambodunum (Kempten), Foetes (Feet), Curia (Chur), Clunia (Feldkirch or Balzers?), Apodiacum (Epfach), Gamundia Romana (Schwäbisch Gmünd), Alae (Aalen), Parthanum (Partenkirchen), Brigantium (Bregenz), and Castra Batava (Passau).