Vicentia was settled by the Italic Euganei tribe and then by the Paleo-Veneti tribe in the 3rd and 2nd centuries BC. The Romans allied themselves with the Paleo-Veneti in their fight against the Celtic tribes that populated north-western Italy. The Roman presence in the area grew exponentially over time and the Paleo-Veneti (whose culture mirrored Etruscan and Greek values more so than Celtic ones) were gradually assimilated. In 157 BC, the city was a de facto Roman centre and was given the name of Vicetia or Vincentia, meaning "victorious".
The citizens of Vicetia received Roman citizenship and were inscribed into the Roman tribe Romilia in 49 BC. The city was known for its agriculture, brickworks, marble quarry, and wool industry and had some importance as a way-station on the important road from Mediolanum (Milan) to Aquileia, near Tergeste (Trieste), but it was overshadowed by its neighbor Patavium (Padua). Little survives of the Roman city, but three of the bridges across the Bacchiglione and Retrone rivers are of Roman origin, and isolated arches of a Roman aqueduct exist outside the Porta Santa Croce.
During the decline of the Western Roman Empire, Heruls, Vandals, Alaric and his Visigoths, as well as the Huns laid waste to the area, but the city recovered after the Ostrogoth conquest in 489 AD, before being conquered by the Byzantine Empire soon after. It was also an important Lombard city and then a Frankish center. Numerous Benedictine monasteries were built in the Vicenza area, beginning in the 6th century.
In 899, Vicenza was destroyed by Magyar raiders.
In 1001, Otto III handed over the government of the city to the bishop, and its communal organization had an opportunity to develop, separating soon from the episcopal authority. It took an active part in the League with Verona and, most of all, in the Lombard League (1164–1167) against Emperor Frederick I Barbarossa compelling Padua and Treviso to join: its podestà, Ezzelino II il Balbo, was captain of the league. When peace was restored, however, the old rivalry with Padua, Bassano, and other cities was renewed, besides which there were the internal factions of the Vivaresi (Ghibellines) and the Maltraversi (Guelphs).
The tyrannical Ezzelino III from Bassano drove the Guelphs out of Vicenza, and caused his brother, Alberico, to be elected podestà (1230). The independent commune joined the Second Lombard League against Emperor Frederick II, and was sacked by that monarch (1237), after which it was annexed to Ezzelino's dominions. On his death the old oligarchic republic political structure was restored – a consiglio maggiore ("grand council") of four hundred members and a consiglio minore ("small council") of forty members – and it formed a league with Padua, Treviso and Verona. Three years later the Vicentines entrusted the protection of the city to Padua, so as to safeguard republican liberty; but this protectorate (custodia) quickly became dominion, and for that reason Vicenza in 1311 submitted to the Scaligeri lords of Verona, who fortified it against the Visconti of Milan.
Vicenza came under rule of Venice in 1404, and its subsequent history is that of Venice. It was besieged by the Emperor Sigismund, and Maximilian I held possession of it in 1509 and 1516.
Early modern era
Vicenza was a candidate to host the Council of Trent.
The 16th century was the time of Andrea Palladio, who left many outstanding examples of his art with palaces and villas in the city's territory, which before Palladio's passage, was arguably the most downtrodden and esthetically lacking city of the Veneto.
After 1797, under Napoleonic rule, it was made a duché grand-fief (not a grand duchy, but a hereditary (extinguished in 1896), nominal duchy, a rare honor reserved for French officials) within Napoleon's personal Kingdom of Italy for general Caulaincourt, also imperial Grand-Écuyer. One of the consequences of the city's occupation was the destruction of a prized silver model of the city, the Jewel of Vicenza.
19th century and later
After 1814, Vicenza passed to the Austrian Empire. In 1848, however, the populace rose against Austria, more violently than in any other Italian centre apart from Milan and Brescia (the city would receive the highest award for military valour for the courage displayed by revolutionaries in this period). As a part of the Kingdom of Lombardy-Venetia, it was annexed to Italy after the Third War of Italian independence.
Vicenza during flooding, November 2010
Vicenza's area was a location of major combat in both World War I (on the Asiago plateau) and World War II (a focal center of the Italian resistance), and it was the most damaged city in Veneto by Allied bombings, including many of its monuments; the civil victims were over 2,000. The end of World War II was followed by a period of depression, caused by the devastation during the two world wars. In the 1960s, the whole central part of Veneto, witnessed a strong economic development caused by the emergence of small and medium family businesses, ranging in a vast array of products (that often emerged illegally) that paved the way for what would be known as the "miracolo del nord-est" ("miracle of the northeast").
In the following years, the economic development grew vertiginously. Huge industrial areas sprouted around the city, massive and disorganized urbanization and employment of foreign immigrants increased.
Vicenza is home to the US Army post Caserma Ederle (Camp Ederle), also known as the U.S. Army Garrison Vicenza. In 1965, Caserma Ederle became the headquarters of the Southern European Task Force, which includes the 173d Airborne Brigade. In January 2006, the European Gendarmerie Force was inaugurated in Vicenza.