Gytheio is located in the northeastern corner of Mani and lies on the northwestern end of the Laconian Gulf. Gytheio was built on a hill called Koumaros or Laryssio in one of the most fertile areas in Mani, near the mouth of the Gythium River, which is usually dry and has been nicknamed Xerias "dry river"; today, most of the Xerias is covered by Ermou Avenue. Further northeast is the delta of the Evrotas River. Offshore are several small islands; the most important of these islands is Cranae, which is connected to the mainland by a causeway. Gytheio is only 40 km (25 mi) southeast of Sparti, connected by Greek National Road 39. The town center is situated around the port. Pine trees are situated in the west and rocky mountains in the north.
The reputed founders of ancient Gythium were Heracles and Apollo, who frequently appear on its coins or in other legends, and Castor and Pollux: the former of these names may point to the influence of Phoenician traders from Tyre, who, we know, visited the Laconian shores at a very early period. It is thought that Gytheio may have been the center of their purple dye trade because the Laconian Gulf had a plentiful source of murex. In classical times it was a community of Perioeci, politically dependent on Sparta, though doubtless with a municipal life of its own.
In 455 BC, during the First Peloponnesian War, it was burned by the Athenian admiral Tolmides who besieged the city with 50 ships and 4,000 hoplites. It was rebuilt and was most probably, the building ground for the Spartan fleet in the Peloponnesian War. In 407 BC during the Peloponnesian War, Alcibiades landed there and saw the thirty triremes the Spartans were building there. In 370 BC, the Thebans under the command of Epaminondas besieged the city successfully for three days after ravaging Laconia. However it was recaptured by the Spartans three days later.
In 219 BC, Philip V of Macedon tried to capture the city but without success. Under Nabis, Gythium became a major naval arsenal and port. During the Roman-Spartan War, Gythium was captured after a lengthy siege. After the war finished, Gythium was made part of the Union of Free Laconians under Achean protection. Nabis recaptured Gythium three years and the Spartan fleet defeated the Achean fleet outside of Gythium. Gythium was liberated by a Roman fleet under the command of Aulus Atilius Serranus.
Subsequently, Gythium formed the most important of the Union of Free Laconians, a group of twenty-four, later eighteen, communities leagued together to maintain their autonomy against Sparta and declared free by Caesar Augustus. The highest officer of the confederacy was the general, who was assisted by a treasurer (rauias), while the chief magistrates of the several communities bore the title of ephors.
In Roman times Gythium remained a major port and it prospered as a member of the Union. As purple dye was popular in Rome, Gythium exported that as well as porphyry and rose antique marble. Evidence of the ancient Gythium prosperity can be found by the fact that the Romans built an ancient theatre which is well preserved today and is still used occasionally. The ancient theatre, as well as the city's Acropolis (west to the location of the theatre) discovered by the archeologist Dimitris Skias on 1891. Some time in the 4th century AD, Gythium was destroyed. What happened to Gythium is not recorded but it is thought to have been either sacked by Alaric and Visigoths, pillaged by the Slavs or destroyed by the massive earthquake that struck the area in 375 AD.
After the earthquake Gythium was abandoned. It remained a small village throughout the Byzantine and Ottoman times. Its importance grew when Tzannetos Grigorakis built his tower at Cranae and more people came and settled at Gytheio. But during the Greek War of Independence, refugees flooded into Mani and made Gytheio a major town.
The modern Gytheio opened a port in the 1960s. Ferries sail from Gytheio to Kythira almost daily and also to Crete twice a week. It is the See of the Diocese of Gytheion and Oitylo, headed by a Metropolitan bishop of the Orthodox Church of Greece. Gytheio is the largest and most important town in Mani. Most of the ruins of ancient Gythium are now submerged in the Laconian Gulf. Some walls' remains can be seen today on the sandy beach of Valtaki and in the shallow waters, where the well known Dimitrios shipwreck lies stranded. It is also the capital of the municipality of Gytheio.
The province of Gytheio (Greek: Επαρχία Γυθείου) was one of the provinces of the Laconia Prefecture. Its territory corresponded with that of the current municipal units Gytheio and East Mani. It was abolished in 2006.
^Roman Gythium:Pausanias has left us a description of the town as it existed in the reign of Marcus Aurelius, the agora, the Acropolis, the island of Cranae (Marathonisi) where Paris celebrated his nuptials with Helen of Troy, the Migonium or precinct of Aphrodite Migonitis (occupied by the modern town), and the hill Larysium (Koumaro) rising above it. The numerous remains extant, of which the theatre and the buildings partially submerged by the sea are the most noteworthy, all belong to the Roman period.