Mljet is the most southerly and easterly of the larger Adriatic islands of the Dalmatia region of Croatia. The National Park includes the western part of the island, Veliko jezero, Malo jezero, Soline Bay and a sea belt 500 m wide from the most prominent cape of Mljet covering an area of 54 km2. The central parts of the park are Veliko jezero with the Isle of St. Mary, Malo jezero and the villages of Goveđari, Polače and Pomena.
Mljet was discovered by ancient Greco-Roman geographers, who wrote the first records and descriptions. The island was first described by Scylax of Caryanda in the 6th century BC; others prefer the text, Periplus of Pseudo-Scylax. In both texts, it is named Melite and supported by Apollonius of Rhodes. Agathemerus and Pliny the Elder call the island Melita. Agesilaus of Anaxarba in Cilicia, the father of Oppian, was banished to Mljet by the Roman Emperor Septimius Severus (AD 145–211) (or to Malta by Lucius Verus: see Oppian).
Mljet has been regarded as the "Melita" on which Saint Paul was shipwrecked (Acts of the Apostles 27:39–28:11), this view being first expounded in the 10th century, by Eastern Roman Emperor Constantine Porphyrogenitus. Saint Paul's shipwreck is generally placed on the Mediterranean island of Malta. Mljet and Malta had the same name in the Greek and Roman sources; the mention of a viper in Acts 28:3–5 was thought to be in favour of Mljet (but there are snakes on both Mljet and Malta). A harbour named after the Saint exists on both islands.
The Benedictines from Pulsano in Apulia became the feudal lords of the island in 1151, having come from Monte Gargano in Italy. They came ashore in the Sutmiholjska cove and in 1187–1198 the Serbian Prince Desa of the House of Vojislavljević built and donated to them the Church and Monastery of Saint Mary on the islet in the Big Lake (Veliko Jezero) towards the north-west end of the island. Pope Innocent III issued a document consecrating the church in 1198.
The Benedictines renounced their rule over Mljet in 1345, keeping only a third of the land. The island got a statute and a municipality in Babino Polje. It was formally annexed by the Republic of Ragusa in 1410. According to the Contract with the Benedictines, the municipality had to pay 300 perpers each year.
In the 16th century, the monastery was the center of the Mljet Congregation (Congregatio Melitensis or Melitana), gathering all the monasteries of Benedictine monks in the area of the Republic of Ragusa. The first president of the Congregation was Mavro Vetranović, the abbot of the Mljet monastery and the famous poet. Another great poet was abbot there—Ignjat Đurđević in the 18th century. As time went by, the Benedictine monastery on Mljet lost its importance, while the seat of the Mljet Congregation moved to Sveti Jakov near Ragusa.
In 1809, during the rule of Napoleon, the Mljet monastery was disbanded. When Austria took over the island, it placed the forestry office in the building. Between the world wars, the building was owned by the Ragusa (Dubrovnik) Bishopric. In 1960 it became a hotel, and in 1998 it was returned to the bishopric.
The island has a long history of eco-damage. In order to ease their transport problems, the monks dug a channel to the south coast, from the lake Veliko Jezero, thus turning both fresh-water lakes into seawater-based ones.
The second incident involves mongooses. Small Asian mongooses were introduced onto the island in the early 20th century in order to reduce the venomous snake population (the island was apparently completely overrun). Whilst the mongooses completed this task, they also disposed of pretty much all the birdlife of the island. To this day, the island is notably short of hedgerow birds such as sparrows. Mongooses are a hazard for domestic poultry, and are also known to cause damage in vineyards and orchards.