During the Greek Revolution of 1821, the island was liberated and became an important base for the re-supplying of the Greek Navy. Administratively, it came under the jurisdiction of the Temporary Committee of the Eastern Sporades.
With the Treaty of London, on 3 February 1830, however, which determined the borders of the newly–established Greek state, the freed islands of the Eastern Sporades were given over to the Ottoman Empire again. In the "Diary of the Prefecture of the Archipelago" of 1886, Leros, along with the islands of Patmos, Lipsos and Fournoi, belonged to the Ottomans. The island's administrative council was made up of both Greeks and Turks.
The Italian Period
In 1912, during the Libyan War against the Ottoman Empire, the Italians occupied all of the Dodecanese islands (except Kastelorizo). On May 12, 1912 the island was seized by the sailors of the Italian Navy cruiser "San Giorgio". The Greek inhabitants of the islands declared the autonomy of the islands under the title "The Aegean State", with the aim of unification with Greece, but with the outbreak of the First World War, these moves came to nothing, and the Italians retained control of the islands.
From 1916 to 1918, the British used Leros as a naval base. In the Venizelos-Tittoni Agreement of 1919, the island was to be returned to Greece, along with all of the Dodecanese except Rhodes, but after the Greek defeat in the Greco-Turkish War the Italians canceled the agreement. As a result, the Treaty of Lausanne confirmed the Italian possession of Leros and the Dodecanese.
The new Italian Fascist regime actively attempted to Italianize the Dodecanese, by making the Italian language compulsory, giving incentives to locals to adopt the Italian nationality, and clamping down on Greek institutions. In the 1930s a new model town, Portolago, was built by the Italian authorities. It is one of the best examples of Italian Rationalist architecture. The Greeks
