The Main metropolis was first mentioned on 22 February 794 in a document of Charlemagne for the Regensburg monastery, St. Emmeram. However, there is proof that the cathedral hill has been under continuous settlement since as early as 3000 BC. At the same place, a Roman military camp was established around 83 AD and in the Merovingian era, the court of a Franconian king. In 843, Frankfurt became at times the most important royal palatinate of the Eastern Franconians and the site of parliaments. In 1220, Frankfurt became a free imperial city. From 1356 onwards, the Golden Bull declared Frankfurt as the permanent city of choice for the Roman kings.
From 1562, the Emperor was also crowned in Frankfurt, the last one being the Habsburg Franz II. After the end of the Holy Roman Empire, Frankfurt joined the Confederation of the Rhine and under the First Prince Karl Theodor of Dalberg, became the capital of a short-lived (1810-1813) grand duchy of Frankfurt.
In 1815, Frankfurt became a free city and the seat of the federal government.
In 1848, the March revolution broke out in the German states. As a symbol of reconciliation, the Franco-Prussian war was officially ended in 1871 with the Peace of Frankfurt. The city expansion of Frankfurt in the 19th century began with the incorporation of Bornheim. Further incorporations followed from 1895 onwards. For a short time, Frankfurt thus became the city with the largest area in Germany. Between 1879 and 1926 important institutions such as the Stock Exchange (1879), the Old Opera (1880), the central station (1888), the University (1914) and the first Frankfurt airport (1926) were built.
Under the National Socialist regime, 9000 Jews were deported from Frankfurt. In World War Two, aerial attacks destroyed almost all of the old and central parts of the city. However, the cityscape that was practically completely in the medieval style up to 1944 – which in this form was unique for a German city at this time – was lost during the modern reconstruction of the city. After the end of the war, the occupying American forces set up their headquarters in the city. Frankfurt then became the administrative headquarters of the trizone. In the voting for the Federal capital, Frankfurt only just lost out narrowly to Konrad Adenauer’s favourite, Bonn. A parliamentary building had already been built in Frankfurt and today houses the Hessischer Rundfunk, the public broadcaster for the state of Hesse. In the post-war period, the city again developed into a business metropolis and in 1998 became the seat of the European Central Bank.