The first traces of settlement in Patras date to as early as the third millennium BC, in the area of modern Aroe. Patras flourished for the first time in the Post-Helladic or Mycenean period (1580–11).
In antiquity Patras remained a farming city. It was in Roman times that it became an important port. After 280 BC and prior to the Roman occupation of Greece, Patras played a significant role in the foundation of the second "Achaean League" (Achaiki Sympoliteia), along with the cities of Dyme, Triteia and Pharai.
Later on, and following the Roman occupation of Greece in 146 BC, Patras played a key role, and Augustus founded a Roman colony in its area.
In addition, Patras has been a Christian centre since the early days of Christianity, and it is the city where St. Andrew was crucified.
In the Byzantine era Patras continued to be an important port as well as an industrial centre. One of the most scholarly philosophers and theologians of the time, Arethas of Caesarea was born at Patrae, at around 860.
By the 9th century there are strong signs the city was prosperous: the widow Danielis from Patras had accumulated immense wealth in land ownership, the carpet and textile industry, and offered critical support in the ascent of Basil I the Macedonian to the Byzantine throne.In 1205 the city was captured by William of Champlitte and Villehardouin, and became a part of the principality of Achaea. It became the seat of the Barony of Patras, and its Latin archbishop primate of the principality.
In 1387 Juan Fernández de Heredia, grand master of the order of the Knights Hospitaller at Rhodes, endeavoured to make himself master of Achaea and took Patras by storm.
In 1408, Patras became Venetian, until it was recaptured in 1430 by the Despotate of Morea and its despot Constantine Palaiologos, who thus succeeded in recovering for the Byzantine Empire the whole of the Morea, apart from Venetian possessions. The administration of Patras was given to George Sphrantzes, while Constantine was immediately contested by the Ottoman Empire and later, in 1449, became emperor of the Byzantine empire.
Patras remained a part of the Despotate of Morea until 1458, when it was conquered by the Sultan of the Ottoman Empire, Mehmet II. Under the Ottomans, it was known as Baliabadra, from the Greek Παλαιά Πάτρα ("Old Patras"), as opposed to Νέα Πάτρα, the town of Ypati in Central Greece. Though Mehmet granted the city special privileges and tax reductions, it never became a major centre of commerce.
Venice and Genoa attacked and captured it several times in the 15th and 16th centuries, but never re-established their rule effectively, except for a period of Venetian rule in 1687–1715.
Patras was one of the first cities in which the Greek Revolution began in 1821; but the Turks, confined to the citadel, held out until 1828. The city was liberated on 7 October 1828 by the French expeditionary force in the Peloponnese, under the command of General Maison.
Patras developed quickly into the second largest urban centre in late 19th century Greece. The city benefited from its role as the main export port for the agricultural produce of the Peloponnese. Italian migrants came to Patras after the failure of Garibaldi.
At the same time, Patras was a gateway for emigration to the USA (most notably following the “raisin crisis” of 1920 which devastated the local economy).
In the early 20th century, Patras developed fast and became the first Greek city to introduce public streetlights and electrified tramways. The war effort necessitated by the first World War hampered the city's development and also created uncontrollable urban sprawl with the influx of refugees from Asia Minor.
In the Second World War the city was a major target of Italian air raids. In the Axis occupation period, a German military command was established and German and Italian troops stationed in the city. After the liberation in October 1944, the city grew fast to recover, but in later years was increasingly overshadowed by the urban pole of Athens.
The city is endowed with a number of neoclassical buildings and mansions dating from the late 19th and early 20th centuries. In the past, years of neglect and the absence of protection enforcement, as well as recent earthquakes, had contributed to the destruction of several such examples.
Today, however, most surviving neoclassical buildings are under a strict protection status. As a part of the 2006 European Capital of Culture programme, there was a project for the restoration of the city's architectural heritage.
Patras' center is characterized by a composition of architectural currents and trends. Α representative example are the façades around the central square of the city (Georgiou I square). The neoclassical Apollo Theatre, a work of Ernst Ziller, is next to the modernist building of the Hall of Literature and Art, while the majority of the unattractive multi-storey buildings on the west and south side of the square were constructed in the late 1960s and 1970s.
Today's Patra is a relatively newly built city, as its medieval buildings were completely destroyed in the Greek War of Independence.
The oldest surviving buildings (apart from ancient monuments and the castle) are the church of Pantocrator in Ano Poli and a residential building (Oikia Tzini) at the corner of Ayiou Nikolaou and Mezonos street, built in 1832. The area on the south of the castle, around the Roman Odeon and the church of Pantokrator, in the Upper Town (Ano Poli), is the most appealing of the city, due to its status as the only area where construction height is limited to two-storey buildings.
Patras is the first city of the modern Greek state to develop a city plan. In January 1829, Stamatis Voulgaris, a Greek engineer of the French army, presented the plan of the new city of Patras to the Governor Kapodistrias, who approved it. Voulgaris applied the orthogonal rule in the urban complex of Patras; the plan was divided into two sectors, the upper and lower city, with a different city block layout.
A revision of the proposal in 1858 was the one finally realised.