Lucius Nasidius (fl.49-31 BC) was a Roman naval commander who fought against Julius Caesar and later against Octavius, suffering defeats on both occasions.
We first hear of Nasidius in the first year of the Great Roman Civil War (49 BC). Caesar had left an army to besiege Massilia while he moved on to Africa. He also built a small fleet, which took part in the blockade of the city. Pompey the Great responded by sending Lucius Nasidius to Massilia to break the blockade, but Nasidius was defeated in the second of two naval battles of Massilia. He fled to the Spanish coast, and then to Africa.
Nasidius is next mentioned in one of Cicero's letters in a way that implies that he commanded some sort of naval force in Africa in 48-47 BC, while Caesar was trapped in Alexandria.
Nasidius is also mentioned in passing in Caesar's commentaries on the African War of 47-46 BC, although both of the mentions in this work could refer to an earlier period.
Nasidius disappears from view until 35 BC, when he reappears as one of the main officers of Sextus Pompey, the son of Pompey the Great. Sextus had nearly achieved great power, fighting a naval war against Octavian and Antony that eventually forced them to make peace with him. This peace had been shorted lived. Pompey was defeated in the naval battle of Naulochus or Mylae, and fled to the east, where he attempted to overthrow Antony. At this point most of his senior supporters, including Nasidius, decided to make their own peace with Antony, leaving Sextus to his fate.
Nasidius appears for one final time, this time as Quintus Nasidius. According to Cassius Dio he commanded part of Antony's fleet in Greece in 31 BC, but was defeated off Patrae by Agrippa before the decisive battle of Actium. After this he disappears from the historical record.