The Adriatic Sea (ancient Adria or Hadria) is an arm of the Mediterranean Sea separating Italy from the Balkan peninsula, and the system of the Apennine mountains from that of the Dinaric Alps and adjacent ranges.
The name, derived from the town of Adria, belonged originally only to the upper portion of the sea (Herodotus vi. 127, vii. 20, ix. 92; Euripides, Hippolytus, 736), but was gradually extended as the Syracusan colonies gained in importance. But even then the Adriatic in the narrower sense only extended as far as the Mons Garganus, the outer portion being called the Ionian Sea: the name was sometimes, however, inaccurately used to include the Gulf of Tarentum (the modern-day Gulf of Taranto) , the Sea of Sicily, the Gulf of Corinth and even the sea between Crete and Malta (Acts xxvii. 27).
The Adriatic extends northwest from 40° to 45° 45' N., with an extreme length of about 480 miles (770 kilometers), and a mean breadth of about 100 miles (160 kilometers), but the Strait of Otranto, through which it connects at the south with the Ionian Sea, is only 45 miles wide. Moreover, the chain of islands which fringes the northern part of the eastern shore reduces the extreme breadth of open sea in this part to 90 miles. Its total surface area is about 60,000 square miles (160,000 square kilometers)
The Italian shore is generally low, merging, in the northwest, into the marshes and lagoons on either hand of the protruding delta of the river Po, the sediment of which has pushed forward the coastline for several miles within historic times -- Adria is now some distance from the shore. On islands within one of the lagoons opening from the Gulf of Venice, Venice has its unique situation. Other notable cities on the Italian coast are Ravenna, Rimini, Bari, and Pescara.
The east coast is generally bold and rocky. South of the Istrian Peninsula, which separates the Gulfs of Venice and Trieste from the Strait of Quarnero, the island-fringe of the east coast extends as far south as Ragusa. The islands, which are long and narrow (the long axis lying parallel with the coast of the mainland), rise rather abruptly to elevations of a few hundred feet, while on the mainland, notably in the magnificent inlet of the Bocche di Cattaro, lofty mountains often fall directly to the sea. This coast, though beautiful, is somewhat sombre, the prevalent colour of the rocks, a light, dead grey, contrasting harshly with the dark vegetation, which on some of the islands is luxuriant. Cities on this coast (and the non-Italian portion of the north shore) include Trieste, Split, and Dubrovnik.
The north part of the sea is very shallow, and between the southern promontories of Istria and Rimini the depth rarely exceeds 25 fathoms. Between Sebenico and Ortona a well-marked depression occurs, a considerable area of which exceeds 100 fathoms in depth. From a point between Curzola and the north shore of the spur of Monte Gargano there is a ridge giving shallower water, and a broken chain of a few islets extends across the sea.
The deepest part of the sea lies east of Monte Gargano, south of Ragusa, and west of Durazzo, where a large basin gives depths of 500 fathoms and upwards, and a small area in the south of this basin falls below 800. The mean depth of the sea is estimated at 133 fathoms.
The bora (northeast wind), and the prevalence of sudden squalls from this quarter or the southeast, are dangers to navigation in winter. Tidal movement is slight.
Both coasts are popular tourist destinations.