Republic of Pisa in the context of "Aragonese conquest of Sardinia"

The history of Italy in the Middle Ages can be roughly defined as the time between the collapse of the Western Roman Empire and the Italian Renaissance. Late antiquity in Italy lingered on into the 7th century under the Ostrogothic Kingdom and the Byzantine Empire under the Justinian dynasty, the Byzantine Papacy until the mid 8th century. The "Middle Ages" proper begin as the Byzantine Empire was weakening under the pressure of the Muslim conquests, and most of the Exarchate of Ravenna finally fell under Lombard rule in 751. From this period, former states that were part of the Exarchate and were not conquered by the Lombard Kingdom, such as the Duchy of Naples, became de facto independent states, having less and less interference from the Eastern Roman Empire.

Lombard rule ended with the invasion of Charlemagne in 773, who established the Kingdom of Italy and the Papal States in large parts of Northern and Central Italy. This set the precedent for the main political conflict in Italy over the following centuries, between the Pope and the Holy Roman Emperor, culminating with conflict between Pope Gregory VII and Henry IV and the latter's "Walk to Canossa" in 1077.

The maritime republics (Italian: repubbliche marinare), also called merchant republics (Italian: repubbliche mercantili), were Italian thalassocratic port cities which, starting from the Middle Ages, enjoyed political autonomy and economic prosperity brought about by their maritime activities. The term, coined during the 19th century, generally refers to four Italian cities, whose coats of arms have been shown since 1947 on the flags of the Italian Navy and the Italian Merchant Navy: Amalfi, Genoa, Pisa, and Venice. In addition to the four best known cities, Ancona, Gaeta, Noli, and, in Dalmatia, Ragusa, are also considered maritime republics; in certain historical periods, they had no secondary importance compared to some of the better known cities.

Uniformly scattered across the Italian peninsula, the maritime republics were important not only for the history of navigation and commerce: in addition to precious goods otherwise unobtainable in Europe, new artistic ideas and news concerning distant countries also spread. From the 10th century, they built fleets of ships both for their own protection and to support extensive trade networks across the Mediterranean, giving them an essential role in reestablishing contacts between Europe, Asia, and Africa, which had been interrupted during the early Middle Ages. They also had an essential role in the Crusades and produced renowned explorers and navigators such as Marco Polo and Christopher Columbus.

Consul (abbrev. cos.; Latin plural consules) was the title of one of the two chief magistrates of the Roman Republic, and subsequently also an important title under the Roman Empire. The title was used in other European city-states through antiquity and the Middle Ages, in particular in the Republics of Genoa and Pisa, then revived in modern states, notably in the First French Republic. The related adjective is consular, from the Latin consularis.

This usage contrasts with modern terminology, where a consul is a type of diplomat.

Alamanno da Costa (active 1193–1224, died before 1229) was a Genoese admiral. He became the count of Syracuse in the Kingdom of Sicily, and led naval expeditions throughout the eastern Mediterranean. He was an important figure in Genoa's longstanding conflict with Pisa and in the origin of its conflict with Venice. The historian Ernst Kantorowicz called him a "famous prince of pirates".

The Duchy of Amalfi (Latin: Ducatus Amalphitanus) or the Republic of Amalfi was a de facto independent state centered on the Southern Italian city of Amalfi during the 10th and 11th centuries. The city and its territory were originally part of the larger Duchy of Naples, governed by a patrician, but it extracted itself from Byzantine vassalage and first elected a duke (or doge) in 958.

During the 10th and 11th centuries Amalfi was estimated to have a population of 50,000–70,000 people. It rose to become an economic powerhouse, a commercial center whose merchants dominated Mediterranean and Italian trade in the ninth and tenth centuries, before being surpassed and superseded by the other maritime republics of the North and the Centre: Pisa, Venice, Genoa, Ancona and Gaeta. In 1073, Amalfi lost its independence, falling to Norman invasion and subsequently to Pisa in 1137.

A maritime nation is any nation that borders the sea and is dependent on its use for the majority of the following state activities: commerce and transport, war, to define a territorial boundary, or for any maritime activity (activities using the sea to convey or produce an end result).

Historically, the term has been used to refer to a thalassocracy such as Carthage and Phoenicia but during the medieval period increasingly became associated with the Maritime Republics of Venice, Pisa, Genoa, Amalfi, Gaeta, Ancona and Ragusa.