Lucius Aelius, adopted son and intended successor of Hadrian (born 101)

Year 138 (CXXXVIII) was a common year starting on Tuesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Niger and Camerinus. The denomination 138 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Lucius Aelius Caesar was the father of Emperor Lucius Verus. In 136, he was adopted by the reigning emperor Hadrian and named heir to the throne. He died before Hadrian and thus never became emperor. After Lucius' death, he was replaced by Antoninus Pius, who succeeded Hadrian the same year.

Hadrian was Roman emperor from 117 to 138. Hadrian was born in Italica, close to modern Seville in Spain, an Italic settlement in Hispania Baetica; his branch of the Aelia gens, the Aeli Hadriani, came from the town of Hadria in eastern Italy. He was a member of the Nerva–Antonine dynasty.

January 1 is the first day of the calendar year in the Gregorian Calendar; 364 days remain until the end of the year. This day is also known as New Year's Day since the day marks the beginning of the year.