During the Tertiary period, the northern part of Puglia was covered by Adriatic Sea. Only the promontory called Promontorio Garganico emerged and it was linked to Tremiti isles and to Pianosa isle. Then, maybe after a cataclysm or because of the erosive action of the sea, the isles detached from the promontory. They still preserved, however, the same features: the caves and the flora, for example. Maybe at the beginning Tremiti were an only big isle, and then they divided into different isles. Several writers of the past confirm these hypotheses. Tremiti isles were already inhabited during Neolithic age. Their ancient name was "Insulae Diomedeae", coming from the Greek God, Diomedes. Diomedes was buried here (he was the son of Tideo, king of Etolia, and of Deifile, daughter of Adrasto, king of Argo). After the death of Adrasto, Diomedes became lord of Argo and king of Etolia. He was considered as the strongest and the most courageous by Greeks. He took part to the Trojan War and he won thanks to his cleverness and intelligence. After the war he went back home and he used stones from the Trojan wall as ballast. When he was home, he discovered that his wife Egialea had betrayed him and so he flew away with his fleet towards West. During a storm in the Adriatic Sea, his ships arrived to Tremiti isles. After his death, Illyrians invaded the archipelago and banished the inhabitants. The souls of the inhabitants were transformed by Venus into birds: they had to be the guardians of their king’s sepulchre (in Italian they are called "diomedee" and live over San Domino). In 8 century a.C. Giulia, Augustus’s niece, died here as an exile. Charles the Great exiled there Paolo Diacono, who succeeded in escaping. The name "Tremitis" is mentioned for the first time in Middle Ages cartography. There are different hypotheses about the origin of the name. Some scholars think it comes from Italian word "terremoto" (Tremetus or Trimerus) (earthquake). Maybe an earthquake made the isles detach from the promontory. Other scholars state that this archipelago was made of an isle and a mountain and then some pieces detached and there was the creation of three isles ("Tre monti", three mountains). During XI century, the Abbey of Tremiti lived a very rich period and annexed a lot of territories on the mainland. But this increasing power annoyed the Abbey of Montecassino that didn’t want to give independence to the Abbey of Tremiti. But the autonomy and the power made moral values fall and in 1237 Cardinal Raniero da Viterbo asked to the Bishop of Termoli to replace the Benedictine order with that of Cistercense coming from Casanova Monastery near Parma. They transformed the abbey into a fortress. But the order disappeared because of the invasions by pirates and the monastery was almost completely destroyed. Pirates coming from Almissa entered the abbey-fortress thanks to a trick. They pretended that their leader had died and asked to bury him on the isle. His coffin was brought in San Nicola Church by pirates (who didn’t bear arms). During the solemn funeral the coffin opened and the leader went out giving also swords to his men. All the friars were killed and the isle remained uninhabited for many years. After this episode, many religious orders refused to move to Tremiti. But in 1412 Pope Gregory XII sent a congregation of Canonici Lateranensi there. The monastery was rebuilt and strengthened, in fact in 1567 it could resist to the attacks of 150 Turk ships. But the monastery began a slow decline and in 1674 it was sold to Celestini Fathers to pay the debts. During the Bourbon period, the king of Naples, Charles III, declared that the monks were only the guardians of the monastery, not the owners, so they couldn't sell it. His successor, Ferdinand IV, in 1782 suppressed the abbey and took all its assets. In 1792 he created a "penal colony" in the abbey and it remained active until 1926. During Napoleonic period the archipelago was occupied by muratians that hid themselves from English armies in San Nicola fortress. In 1843 Ferdinand II King of the Two Sicilies brought to the isles many criminals from Naples. In 1911 around 1300 Libyans were exiled to Tremiti isles because they opposed to Italian colonisation. They died from typhus. In 1987 Muammar Gheddafi declared that, according to him, Tremiti belonged to Libya because they had been inhabited by Libyans in the previous decades. During fascist period, the future Italian president Sandro Pertini, was confined here.