Romanos III Argyros, or Romanus III Argyrus (Greek: Ρωμανός Γ΄ Αργυρός), was Byzantine emperor from 15 November 1028 until his death.
Romanos attracted the attention of Constantine VIII, who forced him to divorce his wife (sending her into a monastery) and to marry the emperor's daughter Zoe Porphyrogenita. The marriage took place on 12 November 1028, and three days later Constantine VIII died, leaving Romanos III as emperor.
The new emperor showed great eagerness to make his mark as a ruler, but was mostly unfortunate in his enterprises. He spent large sums upon new buildings and in endowing the monks. His endeavour to relieve the pressure of taxation disorganized the finances of the state. Idealizing Marcus Aurelius, Romanos aspired to be a new "philosopher king", and similarly desired to imitate the military prowess of Trajan.
At home Romanos III faced several conspiracies, mostly centered on his sister-in-law Theodora, as in 1029 and 1030. Although he survived these attempts on the throne, his early death in 1034 was supposed to have been due to poison administered by his wife, though there is also speculation that he was drowned in a bath on his wife's orders. He was buried in the Church of St. Mary Peribleptos, which he built.