Trajan was born in the municipium of Italica in the present-day Andalusian province of Seville in southern Spain, an Italic settlement in Hispania Baetica; his gens Ulpia came from the town of Tuder in the Umbria region of central Italy.

[26][27] This is confirmed by archeology, with epigraphic evidence placing both the Ulpii and the Traii in Umbria generally and Tuder specifically, and by linguistic studies of the family names Ulpius and Traius which show that both are of Osco-Umbrian origin.

[32] Their son, Trajan's namesake father Marcus Ulpius Traianus, was born at Italica during the reign of Tiberius and became a prominent senator and general, commanding the Legio X Fretensis under Vespasian in the First Jewish-Roman War.

[40] Around this time Trajan brought the architect and engineer Apollodorus of Damascus with him to Rome,[41] and married Pompeia Plotina, a noblewoman from the Roman settlement at Nîmes; the marriage ultimately remained childless.

The details of Trajan's early military career are obscure, save for the fact that in 89, as legate of Legio VII Gemina in Hispania Tarraconensis, he supported Domitian against an attempted coup by Lucius Antonius Saturninus, the governor of Germania Superior.

[64] By not openly supporting Domitian's preference for equestrian officers,[65] Trajan appeared to conform to the idea (developed by Pliny) that an emperor derived his legitimacy from his adherence to traditional hierarchies and senatorial morals.

[68][69] In reality, Trajan did not share power in any meaningful way with the senate, something that Pliny admits candidly: "[E]verything depends on the whims of a single man who, on behalf of the common welfare, has taken upon himself all functions and all tasks".

[76] In short, according to the ethics for autocracy developed by most political writers of the Imperial Roman Age, Trajan was a good ruler in that he ruled less by fear, and more by acting as a role model, for, according to Pliny, "men learn better from examples".

[94] It must be added that, although Trajan was wary of the civic oligarchies in the Greek cities, he also admitted into the senate a number of prominent Eastern notables already slated for promotion during Domitian's reign by reserving for them one of the twenty posts open each year for minor magistrates (the vigintiviri).

[98] Trajan created at least fourteen new senators from the Greek-speaking half of the empire, an unprecedented recruitment number that opens to question the issue of the "traditionally Roman" character of his reign, as well as the "Hellenism" of his successor Hadrian.

[125] Eventually, Dio gained for Prusa the right to become the head of the assize-district, conventus (meaning that Prusans did not have to travel to be judged by the Roman governor), but eleutheria (freedom, in the sense of full political autonomy) was denied.

According to Pliny, the best way to achieve this was to lower the minimum age for holding a seat on the council, making it possible for more sons of the established oligarchical families to join and thus contribute to civic spending; this was seen as preferable to enrolling non-noble wealthy upstarts.

Apollodorus of Damascus' "magnificent" design incorporated a Triumphal arch entrance, a forum space approximately 120 m long and 90m wide, surrounded by peristyles: a monumentally sized basilica: and later, Trajan's Column and libraries.

Its lofty, elevated Imperial viewing box was rebuilt among the seating tiers, so that spectators could see their emperor sharing their enjoyment of the races, alongside his family and images of the gods,[145] At some time during 108 or 109, Trajan held 123 days of games to celebrate his Dacian victory.

[153] The earliest of Trajan's conquests were Rome's two wars against Dacia, an area that had troubled Roman politics for over a decade in regard to the unstable peace negotiated by Domitian's ministers with the powerful Dacian king Decebalus.

[156] Unlike the Germanic tribes, the Dacian kingdom was an organized state capable of developing alliances of its own,[157] thus making it a strategic threat and giving Trajan a strong motive to attack it.

A controversial scene on Trajan's column just before the fall of Sarmizegetusa Regia suggests that Decebalus may have offered poison to his remaining men as an alternative option to capture or death while trying to flee the besieged capital with him.

[172] This may have been intended as a basis for further expansion within Eastern Europe, as the Romans believed the region to be much more geographically "flattened", and thus easier to traverse, than it actually was; they also underestimated the distance from those vaguely defined borders to the ocean.

[186] Defence of the province was entrusted to a single legion, the XIII Gemina, stationed at Apulum, which functioned as an advance guard that could, in case of need, strike either west or east at the Sarmatians living at the borders.

[192] The victory was commemorated by the construction both of the 102 cenotaph generally known as the Tropaeum Traiani in Moesia, as well of the much later (113) Trajan's Column in Rome, the latter depicting in stone carved bas-reliefs the Dacian Wars' most important moments.

[194] In 113, Trajan embarked on his last campaign, provoked by Parthia's decision to put an unacceptable king on the throne of Armenia, a kingdom over which the two great empires had shared hegemony since the time of Nero some fifty years earlier.

[198] As the surviving literary accounts of Trajan's Parthian War are fragmentary and scattered,[199] it is difficult to assign them a proper context, something that has led to a long-running controversy about its precise happenings and ultimate aims.

[232] At the same time, a Roman column under the legate Lusius Quietus – an outstanding cavalry general[233] who had signalled himself during the Dacian Wars by commanding a unit from his native Mauretania[234] – crossed the Araxes river from Armenia into Media Atropatene and the land of the Mardians (present-day Ghilan).

[237] The chronology of subsequent events is uncertain, but it is generally believed that early in 115 Trajan launched a Mesopotamian campaign, marching down towards the Taurus mountains in order to consolidate territory between the Tigris and Euphrates rivers.

[243] After wintering in Antioch during 115/116  – and, according to literary sources, barely escaping from a violent earthquake that claimed the life of one of the consuls, Marcus Pedo Virgilianus[244][245] – Trajan again took to the field in 116, with a view to the conquest of the whole of Mesopotamia, an overambitious goal that eventually backfired on the results of his entire campaign.

[261] Trajan left the Persian Gulf for Babylon – where he intended to offer sacrifice to Alexander in the house where he had died in 323 BC[262] –  But a revolt led by Sanatruces, a nephew of the Parthian king Osroes I who had retained a cavalry force, possibly strengthened by the addition of Saka archers,[263] imperilled Roman positions in Mesopotamia and Armenia.

[264] About this same time (AD 116–117), Jews in the Eastern provinces of the Roman Empire—Egypt, Cyprus, and Cyrene, which was likely the original trouble hotspot—rebelled in what appears to have been an ethnic and religious uprising against the local populations, later known as the Diaspora Revolt.

[270][278] In contrast, the next prominent Roman figure in charge of the repression of the Jewish revolt, the equestrian Quintus Marcius Turbo, who had dealt with the rebel leader from Cyrene, Loukuas, retained Hadrian's trust, eventually becoming his Praetorian Prefect.

32 f. and 73 f.[312] In the 18th century, King Charles III of Spain commissioned Anton Raphael Mengs to paint The Triumph of Trajan on the ceiling of the banquet hall of the Royal Palace of Madrid – considered among the best works of this artist.

[318] Following in Paribeni's footsteps, the German historian Alfred Heuss saw in Trajan "the accomplished human embodiment of the imperial title" (die ideale Verkörperung des humanen Kaiserbegriffs).