They are the Big 4 Sailors: Venice (Aph Italy/North Italy), Genoa, Pisa and Amalfi.

Pisa and Genoa have been like an old married couple since the Middle Ages. They married somewhere in the Middle Ages without telling anyone. They're always fighting, always arguing, but never let anyone outside attack one of them without the other's consent. They'd tear them to pieces.

Genoa and Venice have been rivals since the Middle Ages to see who could secure the best deals and trade routes. However, they did occasionally help each other out.

Pisa and Amalfi dated for a while when they were teenagers. Pisa was a much better sailor than Amalfi, which made him jealous and envious. She dethroned him as the most important port in the medieval Italian peninsula. He has never surpassed her and detests Genoa for marrying her.

Venice and Pisa had a rivalry in the past, but nothing compared to their clashes with Genoa. However, since Pisa became a satellite city of Florence, its importance and prestige declined, leaving its routes to Genoa. Pisa suffered a similar fate with Genoa as Amalfi suffered with Venice, but to a much lesser extent.

Amalfi and Venice competed for the best routes with Byzantium, but without open warfare. When Amalfi was conquered by the Normans in 1137, Venice acquired all its routes and colonies.

Genoa and Amalfi ignored each other's existence.