During ancient Rome, a settlement of unknown name existed at the site of Heidelberg. It consisted of a fort founded around 70 AD in the present-day district of Neuenheim and a civilian settlement (vicus) that developed around the fort and also extended into the present-day district of Bergheim. The original wooden military camp was replaced by a stone fort around the year 90. In 80/90 there was a wooden bridge over the Neckar, and in 200 there was a bridge built on stone pillars. Even after the garrison of the Heidelberg fort was withdrawn around the year 135, the civilian settlement continued to flourish thanks to its favorable geographical location and developed into a prosperous pottery center. Nevertheless, Heidelberg always remained in the shadow of neighboring Lopodunum (today Ladenburg), which was the main city of the region at the time. As a result of the Alamanni invasions, Roman Heidelberg was abandoned in the 3rd century as part of the so-called Limesfall.

Topography and name

Heidelberg is located where the Neckar flows from the Odenwald into the Upper Rhine Plain. Located around 20 kilometers before the Neckar flows into the Rhine, Heidelberg belongs to the right area of the Rhine. The location at the intersection of the Neckar and the Bergstraße running along the edge of the mountains is extremely favorable in terms of transport geography. While the old town, the nucleus of today's city, lies wedged between the river and the mountains on the alluvial fan of the Klingenteich stream, people, before the Middle Ages, avoided the narrow and flood-prone river valley and preferred the fertile plain as a place to settle thanks to the loess soil. The 440-metre-high Heiligenberg, which rises opposite the old town on the edge of the Odenwald, has also attracted people for thousands of years due to its favorable sheltered location. Heidelberg during the Roman period was located just under two kilometers west of the old town in the plain on the north shore of the Neckar in today's Neuenheim district. The opposite shore of the Neckar in Bergheim was also inhabited in Roman times. Heidelberg's name during the Roman period is unknown. It is impossible to say whether the Romans adopted an old Celtic toponym or gave the place a Latin name. Suggestions such as Traiectum ad Nicrem ("Neckar Crossing"; analogous to Traiectum ad Mosam, today Maastricht)Tilmann Bechert: Die Frühzeit bis zu den Karolingern, in: Elmar Mittler (ed.): Heidelberg. Geschichte und Gestalt, Heidelberg 1996, p. 31. must be considered purely speculative. Rufiana, mentioned by the ancient geographer Claudius Ptolemy as the site of a fort, is now associated with Ludwigshafen-Rheingönheim. Piri Mons, which has also been suggested, was the name of an unknown mountain on the right area of the Rhine, possibly Heiligenberg in Heidelberg, but not the settlement on the site of Heidelberg.

Pre-Roman period The area that is now Heidelberg has been permanently settled since the Neolithic period. The Celts were the predecessors of the Romans in the Heidelberg area during the Latène period. According to the ancient authors Ptolemy and Tacitus, the Celtic inhabitants of southwestern Germany were members of the Helvetii tribe. In the 5th century BC, the Celts founded a fortified city (oppidum) on the top of the Heiligenberg. Two centuries later, for reasons unknown, the settlement on the hill was abandoned. There were numerous small Celtic settlements on both sides of the Neckar River in the plain at the foot of the mountain. There were numerous small Celtic settlements on both sides of the Neckar, in the plain at the foot of the mountain. In the 1st century BC, the Helvetii gave up their ancestral homes under pressure from the advancing Germanic tribe of the Suebi under Ariovistus. In Heidelberg, this can be seen in the abrupt destruction of archaeological finds from the late Latène Period.Bechert 1996, p. 28.

Neckar Suebians

After their mass emigration, the Helvetii tried to gain a foothold in Gaul. This served Gaius Iulius Caesar as a reason for the Gallic War. In 58 BC, the Romans under Caesar defeated the Helvetii at Bibracte, conquered Gaul by 51 BC, and advanced as far as the Rhine. The area east of the Rhine, known as Agri decumates, remained largely uninhabited for almost a century and is described by Ptolemy as a "Helvetic wasteland". After the attempt to conquer Germania, which had begun under Augustus, had failed, the Romans expanded the Rhine as an external border from 17 AD during the reign of Emperor Tiberius and began to settle Germanic ethnic groups loyal to Rome in the area on the right of the Rhine to protect the Rhine border. A sub-tribe of the Suebians settled on the lower reaches of the Neckar. The Neckar Suebians were given the status of a civitas and were thus integrated into the Roman administrative system. The main town of the Civitas Ulpia Sueborum Nicrensium was Lopodunum, today's Ladenburg.

The Neckar Suebians initially retained their Elbe-Germanic culture and settled in their own village communities. In Heidelberg, Neckar Suebian villages can be found in the present-day districts of Bergheim, Wieblingen, and Kirchheim.Renate Ludwig: Kelten, Kastelle und Kurfürsten. Archäologie am Unteren Neckar. Theiss, Stuttgart 1997, , p. 37. Under the influence of Roman culture, the Neckar Suebians were Romanized until the 2nd century.

Incorporation into the Roman Empire

The final incorporation of Heidelberg into the Roman Empire and the construction of the Roman fort took place under Emperor Vespasian (69–79). After the latter had emerged victorious from the turmoil of the Four Emperors' Year and had put down the Batavian Uprising on the Lower Rhine in the year 70, he had the Kinzig road built in 73/74, to shorten the approach route from the Danube to the Middle and Lower Rhine. At the same time, the Roman army was also pushed eastwards along the northern Upper Rhine. The Romans replaced the Neckarsuebian militia with their troops and built several forts to secure the border: In addition to Heidelberg, new forts were built in Aquae (Baden-Baden), Lopodunum (Ladenburg), and Groß-Gerau.

In Heidelberg, the first fort, called Ostkastell, was abandoned after just a few years and relocated a few hundred meters to the west. The wooden west fort built in 74 was destroyed by fire and replaced by a stone fort on the same site around the year 90. The first pile bridge over the Neckar was built around 80/90.Renate Ludwig: Kelten, Kastelle und Kurfürsten. Archäologie am Unteren Neckar. Theiss, Stuttgart 1997, , p. 44 ff. Settlements (vici) developed around the fort on both sides of the Neckar, which soon grew and prospered economically thanks to Heidelberg's favorable geographical location.

In 85, the army districts of the Upper and Lower Rhine were converted into civilian provinces. As a result, Heidelberg became part of the province of Germania Superior (Upper Germania), whose capital was Mogontiacum (Mainz). In response to an uprising by the provincial governor Lucius Antonius Saturninus in Mogontiacum, the Romans considered it necessary to further improve the traffic situation between the Rhine and the Danube. For this reason, at the same time as the construction of the Neckar-Odenwald Limes, a new military road was probably built between Mogontiacum and Augusta Vindelicum (Augsburg) between 100 and 120. This route also passed through Heidelberg and crossed the Neckar.

In the 2nd century, the Roman border was pushed forward again with the construction of the Upper Germanic-Rhaetian Limes. Around 135, the unit previously stationed in Heidelberg was withdrawn and relocated to the Limes in Butzbach in the Wetterau region. However, the civilian settlement continued to prosper after the soldiers left. The old wooden bridge was replaced by a stone pillar construction around the year 200.

Germanic invasions and Roman retreat In the 3rd century, the Roman Empire experienced a serious imperial crisis when external threats and internal unrest shook the Roman state. In the east, the Romans were threatened by the Persian Sasanian Empire, on the Danube the Goths exerted pressure, and on the Rhine was an onslaught by the Alemanni. In 233, this Germanic tribe overran the Limes for the first time and raided Roman territory. Despite several campaigns against the Alamanni, the Roman emperors were unable to stabilize the situation, with the result that raids and pillaging became more frequent in Upper Germania over the next few decades. At the same time as the usurpation of Postumus, who founded a special Gallic Empire in 260, there was a devastating invasion by the Alamanni, Franks, and Juthungi. Around 260/70, the Romans were forced to abandon the Limes and withdrew to the Rhine and the Danube (Limesfall). Although Emperor Diocletian (284–305) succeeded in consolidating the Roman Empire, the provincial territory on the right territory of the Rhine was finally lost.

Heidelberg was also affected by the Alamannic raids. Archaeological evidence shows that the vicus burned down several times around the middle of the 3rd century - presumably as a result of the Alamanni pillaging it. In response to the invasions, the gate towers of the stone fort were reinforced. Evidence of the crisis can also be seen in the finds of a pottery and metal deposit in a Roman cellar as well as a coin hoard, which was buried at the west gate of the fort in the 1930s for fear of the Germanic tribes and was never dug up again.Renate Ludwig: Kelten, Kastelle und Kurfürsten. Archäologie am Unteren Neckar. Theiss, Stuttgart 1997, , p. 104 ff. A milestone from the year 253. is the latest known Roman inscription in Heidelberg and (together with another milestone from Lopodunum) in the Upper German region on the right territory of the Rhine.Hans Ulrich Nuber: Staatskrise im 3. Jahrhundert. Die Aufgabe der rechtsrheinischen Gebiete, in: Imperium Romanum – Roms Provinzen an Neckar, Rhein und Donau, Stuttgart 2005, here p. 442. The military site in Heidelberg was finally abandoned at the latest when the Romans withdrew from the Limes.Renate Ludwig: Kelten, Kastelle und Kurfürsten. Archäologie am Unteren Neckar. Theiss, Stuttgart 1997, , p. 49.

Post-Roman period

After the abandonment of the Limes, the Alamanni began to colonize the vacated land, as evidenced by grave finds from the 4th and 5th centuries in Heidelberg.Renate Ludwig: Kelten, Kastelle und Kurfürsten. Archäologie am Unteren Neckar. Theiss, Stuttgart 1997, , p. 108. However, the Roman fort and vicus were abandoned and the bridge fell into disrepair. Unlike in neighboring Lopodunum, where the Romans built a burgus as a military bridgehead on the right territory of the Rhine as late as the 4th century, the Romans did not rebuild their presence in Heidelberg. The oldest parts of Heidelberg date back to village foundations from the time of the Frankish colonisation in the 6th century, while the actual city was only founded in the Middle Ages at the foot of the castle and was first mentioned in 1196. There is therefore no continuity between the ancient settlement in the Heidelberg area and the history of today's city, which began in the Middle Ages.

Structures

Fort