John the Lydian or John Lydus (Greek: Ἰωάννης Λαυρέντιος ὁ Λυδός; Latin: Joannes Laurentius Lydus) was a 6th-century Byzantine administrator and writer on antiquarian subjects.
He was born in 490 AD at Philadelphia in Lydia, whence his cognomen "Lydus". At an early age he set out to seek his fortune in Constantinople, and held high court and state offices in the praetorian prefecture of the East under Anastasius and Justinian. In 552 he lost favour, and was dismissed. The date of his death is not known, but he was probably alive during the early years of Justin II (reigned 565–578).
During his retirement he occupied himself in the compilation of works on the antiquities of Rome, three of which have been preserved:
Lydus or Lydos is an adjective or a name based on the adjective for a person or other object from ancient Lydia. It can mean: