Barcelona is a city in Spain. It is the capital and largest city of Catalonia, as well as the second most populous municipality of Spain. With a population of 1.6 million within city limits, its urban area extends to numerous neighbouring municipalities within the Province of Barcelona and is home to around 4.8 million people, making it the sixth most populous urban area in the European Union after Paris, London, Madrid, the Ruhr area and Milan. It is one of the largest metropolises on the Mediterranean Sea, located on the coast between the mouths of the rivers Llobregat and Besòs, and bounded to the west by the Serra de Collserola mountain range, the tallest peak of which is 512 metres (1,680 feet) high.

Founded as a Roman city, in the Middle Ages Barcelona became the capital of the County of Barcelona. After merging with the Kingdom of Aragon, Barcelona continued to be an important city in the Crown of Aragon as an economic and administrative centre of this Crown and the capital of the Principality of Catalonia. Barcelona has a rich cultural heritage and is today an important cultural centre and a major tourist destination. Particularly renowned are the architectural works of Antoni Gaudí and Lluís Domènech i Montaner, which have been designated UNESCO World Heritage Sites. The headquarters of the Union for the Mediterranean are located in Barcelona. The city is known for hosting the 1992 Summer Olympics as well as world-class conferences and expositions and also many international sport tournaments.

Barcelona is one of the world's leading tourist, economic, trade fair and cultural centres, and its influence in commerce, education, entertainment, media, fashion, science, and the arts all contribute to its status as one of the world's major global cities. It is a major cultural and economic centre in southwestern Europe, 24th in the world (before Zürich, after Frankfurt) and a financial centre. In 2008 it was the fourth most economically powerful city by GDP in the European Union and 35th in the world with GDP amounting to €177 billion. In 2012 Barcelona had a GDP of $170 billion; and it was leading Spain in employment rate in that moment.

In 2009 the city was ranked Europe's third and one of the world's most successful as a city brand. In the same year the city was ranked Europe's fourth best city for business and fastest improving European city, with growth improved by 17% per year, and the city has been experiencing strong and renewed growth for the past three years. Since 2011 Barcelona has been a leading smart city in Europe. Barcelona is a transport hub, with the Port of Barcelona being one of Europe's principal seaports and busiest European passenger port, an international airport, Barcelona–El Prat Airport, which handles over 50 million passengers per year, an extensive motorway network, and a high-speed rail line with a link to France and the rest of Europe.

Rome is the capital city and a special comune of Italy (named Comune di Roma Capitale). Rome also serves as the capital of the Lazio region. With 2,872,800 residents in 1,285 km2(496.1 sq mi), it is also the country's most populated comune. It is the fourth-most populous city in the European Union by population within city limits. It is the centre of the Metropolitan City of Rome, which has a population of 4,355,725 residents, thus making it the most populous metropolitan city in Italy. Rome is located in the central-western portion of the Italian Peninsula, within Lazio (Latium), along the shores of the Tiber. The Vatican City (the smallest country in the world) is an independent country inside the city boundaries of Rome, the only existing example of a country within a city: for this reason Rome has been often defined as capital of two states.

Rome's history spans 28 centuries. While Roman mythology dates the founding of Rome at around 753 BC, the site has been inhabited for much longer, making it one of the oldest continuously occupied sites in Europe. The city's early population originated from a mix of Latins, Etruscans, and Sabines. Eventually, the city successively became the capital of the Roman Kingdom, the Roman Republic and the Roman Empire, and is regarded as the birthplace of Western civilization and by some as the first ever metropolis. It was first called The Eternal City (Latin: Urbs Aeterna; Italian: La Città Eterna) by the Roman poet Tibullus in the 1st century BC, and the expression was also taken up by Ovid, Virgil, and Livy. Rome is also called the "Caput Mundi" (Capital of the World). After the fall of the Western Empire, which marked the beginning of the Middle Ages, Rome slowly fell under the political control of the Papacy, which had settled in the city since the 1st century AD, until in the 8th century it became the capital of the Papal States, which lasted until 1870. Beginning with the Renaissance, almost all the popes since Nicholas V (1447–1455) pursued over four hundred years a coherent architectural and urban programme aimed at making the city the artistic and cultural centre of the world. In this way, Rome became first one of the major centres of the Italian Renaissance, and then the birthplace of both the Baroque style and Neoclassicism. Famous artists, painters, sculptors and architects made Rome the centre of their activity, creating masterpieces throughout the city. In 1871, Rome became the capital of the Kingdom of Italy, which, in 1946, became the Italian Republic.

Rome has the status of a global city. In 2016, Rome ranked as the 14th-most-visited city in the world, 3rd most visited in the European Union, and the most popular tourist attraction in Italy. Its historic centre is listed by UNESCO as a World Heritage Site. The famous Vatican Museums are among the world's most visited museums while the Colosseum was the most popular tourist attraction in world with 7.4 million visitors in 2018. Host city for the 1960 Summer Olympics, Rome is the seat of several specialized agencies of the United Nations, such as the Food and Agriculture Organization (FAO), the World Food Programme (WFP) and the International Fund for Agricultural Development (IFAD). The city also hosts the Secretariat of the Parliamentary Assembly of the Union for the Mediterranean (UfM) as well as the headquarters of many international business companies such as Eni, Enel, TIM, Leonardo S.p.A., and national and international banks such as Unicredit and BNL. Its business district, called EUR, is the base of many companies involved in the oil industry, the pharmaceutical industry, and financial services. Rome is also an important fashion and design centre thanks to renowned international brands centered in the city. Rome's Cinecittà Studios have been the set of many Academy Award–winning movies.

Genoa is the capital of the Italian region of Liguria and the sixth-largest city in Italy. In 2015, 594,733 people lived within the city's administrative limits. As of the 2011 Italian census, the Province of Genoa, which in 2015 became the Metropolitan City of Genoa, counted 855,834 resident persons. Over 1.5 million people live in the wider metropolitan area stretching along the Italian Riviera.

 Located on the Gulf of Genoa in the Ligurian Sea, Genoa has historically been one of the most important ports on the Mediterranean: it is currently the busiest in Italy and in the Mediterranean Sea and twelfth-busiest in the European Union. Genoa has been nicknamed la Superba ("the proud one") due to its glorious past and impressive landmarks. Part of the old town of Genoa was inscribed on the World Heritage List (UNESCO) in 2006 as Genoa: Le Strade Nuove and the system of the Palazzi dei Rolli. The city's rich cultural history in art, music and cuisine allowed it to become the 2004 European Capital of Culture. It is the birthplace of Christopher Columbus, Andrea Doria, Niccolò Paganini, Giuseppe Mazzini, Renzo Piano and Grimaldo Canella, founder of the House of Grimaldi, among others.

Genoa, which forms the southern corner of the Milan-Turin-Genoa industrial triangle of Northwest Italy, is one of the country's major economic centers. The city has hosted massive shipyards and steelworks since the 19th century, and its solid financial sector dates back to the Middle Ages. The Bank of Saint George, founded in 1407, is among the oldest in the world and has played an important role in the city's prosperity since the middle of the 15th century. Today a number of leading Italian companies are based in the city, including Fincantieri, Selex ES, Ansaldo Energia, Ansaldo STS, Edoardo Raffinerie Garrone, Piaggio Aerospace, Mediterranean Shipping Company and Costa Cruises.

Marseille is the second-largest city of France. The main city of the historical province of Provence, it nowadays is the prefecture of the department of Bouches-du-Rhône and region of Provence-Alpes-Côte d'Azur. It is located on France's south coast near the mouth of the Rhône river. The city covers an area of 241 km2 (93 sq mi) and had a population of 852,516 in 2012. Its metropolitan area, which extends over 3,173 km2 (1,225 sq mi) is the third-largest in France after Paris and Lyon, with a population of 1,831,500 as of 2010.

 Known to the ancient Greeks and Romans as Massalia, Marseille was an important European trading centre and remains the main commercial port of the French Republic. Marseille is now France's largest city on the Mediterranean coast and the largest port for commerce, freight and cruise ships. The city was European Capital of Culture in 2013 and European Capital of Sport in 2017; it hosted matches at the 1998 World Cup and Euro 2016. It is home to Aix-Marseille University.

Alicante, or Alacant , both the Spanish and Valencian being official names, is a city and port in Spain on the Costa Blanca, the capital of the province of Alicante and of the comarca of Alacantí, in the south of the Valencian Community. It is also a historic Mediterranean port. The population of the city of Alicante proper was 330,525, estimated as of 2016, ranking as the second-largest Valencian city. Including nearby municipalities, the Alicante conurbation had 452,462 residents. The population of the metropolitan area (including Elche and satellite towns) was 757,085 as of 2014 estimates, ranking as the eighth-largest metropolitan area of Spain.