The first urban settlement on the grounds of modern-day Cologne was Oppidum Ubiorum, founded in 38 BC by the Ubii, a Cisrhenian Germanic tribe. In 50 AD, the Romans founded Colonia Claudia Ara Agrippinensium (Cologne) on the river Rhine and the city became the provincial capital of Germania Inferior in 85 AD. Considerable Roman remains can be found in present-day Cologne, especially near the wharf area, where a 1,900-year-old Roman boat was discovered in late 2007. From 260 to 271 Cologne was the capital of the Gallic Empire under Postumus, Marius, and Victorinus. In 310 under emperor Constantine I a bridge was built over the Rhine at Cologne. Roman imperial governors resided in the city and it became one of the most important trade and production centres in the Roman Empire north of the Alps. Cologne is shown on the 4th century Peutinger Map.
Maternus, who was elected as bishop in 313, was the first known bishop of Cologne. The city was the capital of a Roman province until it was occupied by the Ripuarian Franks in 462. Parts of the original Roman sewers are preserved underneath the city, with the new sewerage system having opened in 1890.
Early medieval Cologne was part of Austrasia within the Frankish Empire. In 716, Charles Martel commanded an army for the first time and suffered the only defeat of his life when Chilperic II, King of Neustria, invaded Austrasia and the city fell to him in the Battle of Cologne. Charles fled to the Eifel mountains, rallied supporters, and took the city back that same year after defeating Chilperic in the Battle of Amblève.
Cologne had been the seat of a bishop since the Roman period; under Charlemagne, in 795, bishop Hildebold was promoted to archbishop. In 843, Cologne became a city within the Treaty of Verdun-created East Francia.
In 953, the archbishops of Cologne first gained noteworthy secular power, when bishop Bruno was appointed as duke by his brother Otto I, King of Germany. In order to weaken the secular nobility, who threatened his power, Otto endowed Bruno and his successors on the bishop's see with the prerogatives of secular princes, thus establishing the Electorate of Cologne, formed by the temporal possessions of the archbishopric and included in the end a strip of territory along the left Bank of the Rhine east of Jülich, as well as the Duchy of Westphalia on the other side of the Rhine, beyond Berg and Mark.
By the end of the 12th century, the Archbishop of Cologne was one of the seven electors of the Holy Roman Emperor. Besides being prince elector, he was Arch-chancellor of Italy as well, technically from 1238 and permanently from 1263 until 1803.
Following the Battle of Worringen in 1288, Cologne gained its independence from the archbishops and became a Free City. Archbishop Sigfried II von Westerburg was forced into exile in Bonn.
The archbishop nevertheless preserved the right of capital punishment. Thus the municipal council (though in strict political opposition towards the archbishop) depended upon him in all matters concerning criminal justice. This included torture, which sentence was only allowed to be handed down by the episcopal judge, the so-called "Greve". This legal situation lasted until the French conquest of Cologne.
Besides its economic and political significance Cologne also became an important centre of medieval pilgrimage, when Cologne's Archbishop Rainald of Dassel gave the relics of the Three Wise Men to Cologne's cathedral in 1164 (after they, in fact, had been captured from Milan). Besides the three magi Cologne preserves the relics of Saint Ursula and Albertus Magnus.
Cologne's location on the river Rhine placed it at the intersection of the major trade routes between east and west as well as the main Western Europe trade route, South – North Northern Italy-Flanders. These two trade routes were the basis of Cologne's growth. By 1300 the city population was 50,000-55,000. Cologne was a member of the Hanseatic League in 1475, when Frederick III confirmed the city's imperial immediacy.
Early modern history
The economic structures of medieval and early modern Cologne were characterised by the city's status as a major harbour and transport hub on the Rhine. Craftsmanship was organised by self-administering guilds, some of which were exclusive to women.
As a free city, Cologne was a sovereign state within the Holy Roman Empire and as such had the right (and obligation) to maintain its own military force. As they wore a red uniform, these troops were known as the Rote Funken (red sparks). These soldiers were part of the Army of the Holy Roman Empire ("Reichskontingent") and fought in the wars of the 17th and 18th century, including the wars against revolutionary France, when the small force was almost completely wiped out in combat. The tradition of these troops is preserved as a military persiflage by Cologne's most outstanding carnival society, the Rote Funken.
The free city of Cologne must not be confused with the Archbishopric of Cologne which was a state of its own within the Holy Roman Empire. Since the second half of the 16th century the archbishops were drawn from the Bavaria Wittelsbach dynasty. Due to the free status of Cologne, the archbishops were usually not allowed to enter the city. Thus they took up residence in Bonn and later in Brühl on the Rhine. As members of an influential and powerful family, and supported by their outstanding status as electors, the archbishops of Cologne repeatedly challenged and threatened the free status of Cologne during the 17th and 18th centuries, resulting in complicated affairs, which were handled by diplomatic means and propaganda as well as by the supreme courts of the Holy Roman Empire.
From the 19th century until World War II
Cologne lost its status as a free city during the French period. According to the Peace Treaty of Lunéville (1801) all the territories of the Holy Roman Empire on the left bank of the Rhine were officially incorporated into the French Republic (which had already occupied Cologne in 1794). Thus this region later became part of Napoleon's Empire. Cologne was part of the French Département Roer (named after the river Roer, German: Rur) with Aachen (French: Aix-la-Chapelle) as its capital. The French modernised public life, for example by introducing the Napoleonic code and removing the old elites from power. The Napoleonic code remained in use on the left bank of the Rhine until 1900, when a unified civil code (the Bürgerliches Gesetzbuch) was introduced in the German Empire. In 1815 at the Congress of Vienna, Cologne was made part of the Kingdom of Prussia, first in the Jülich-Cleves-Berg province and then the Rhine province.
The permanent tensions between the Roman Catholic Rhineland and the overwhelmingly Protestant Prussian state repeatedly escalated with Cologne being in the focus of the conflict. In 1837 the archbishop of Cologne, Clemens August von Droste-Vischering, was arrested and imprisoned for two years after a dispute over the legal status of marriages between Protestants and Roman Catholics (Mischehenstreit). In 1874, during the Kulturkampf, Archbishop Paul Melchers was imprisoned before taking asylum in the Netherlands. These conflicts alienated the Catholic population from Berlin and contributed to a deeply felt anti-Prussian resentment, which was still significant after World War II, when the former mayor of Cologne, Konrad Adenauer, became the first West German chancellor.
During the 19th and 20th centuries, Cologne absorbed numerous surrounding towns, and by World War I had already grown to 700,000 inhabitants. Industrialisation changed the city and spurred its growth. Vehicle and engine manufacturing was especially successful, though the heavy industry was less ubiquitous than in the Ruhr area. The cathedral, started in 1248 but abandoned around 1560, was eventually finished in 1880 not just as a place of worship but also as a German national monument celebrating the newly founded German empire and the continuity of the German nation since the Middle Ages. Some of this urban growth occurred at the expense of the city's historic heritage with much being demolished (for example, the city walls or the area around the cathedral) and sometimes replaced by contemporary buildings.
Cologne was designated as one of the Fortresses of the German Confederation. It was turned into a heavily armed fortress (opposing the French and Belgian fortresses of Verdun and Liège) with two fortified belts surrounding the city, the remains of which can be seen to this day. The military demands on what became Germany's largest fortress presented a significant obstacle to urban development, with forts, bunkers, and wide defensive dugouts completely encircling the city and preventing expansion; this resulted in a very densely built-up area within the city itself.
During World War I Cologne was the target of several minor air raids but suffered no significant damage. Cologne was occupied by the British Army of the Rhine until 1926, under the terms of the Armistice and the subsequent Versailles Peace Treaty.
In contrast with the harsh behaviour of the French occupation troops in Germany, the British forces were more lenient to the local population. Konrad Adenauer, the mayor of Cologne from 1917 until 1933 and later a West German chancellor, acknowledged the political impact of this approach, especially since Britain had opposed French demands for a permanent Allied occupation of the entire Rhineland.
As part of the demilitarisation of the Rhineland, the city's fortifications had to be dismantled. This was an opportunity to create two green belts (Grüngürtel) around the city by converting the fortifications and their fields of fire into large public parks. This was not completed until 1933. In 1919 the University of Cologne, closed by the French in 1798, was reopened. This was considered to be a replacement for the loss of the University of Strasbourg on the west bank of the Rhine, which reverted to France with the rest of Alsace. Cologne prospered during the Weimar Republic (1919–33), and progress was made especially in public governance, city planning, housing and social affairs. Social housing projects were considered exemplary and were copied by other German cities. Cologne competed to host the Olympics, and a modern sports stadium was erected at Müngersdorf. When the British occupation ended, the prohibition of civil aviation was lifted and Cologne Butzweilerhof Airport soon became a hub for national and international air traffic, second in Germany only to Berlin Tempelhof Airport.
The democratic parties lost the local elections in Cologne in March 1933 to the Nazi Party and other right wing parties. The Nazis then arrested the Communist and Social Democrats members of the city assembly, and Mayor Adenauer was dismissed. Compared to some other major cities, however, the Nazis never gained decisive support in Cologne. (Significantly, the number of votes cast for the Nazi Party in Reichstag elections had always been the national average.) By 1939 the population had risen to 772,221 inhabitants.
World War II
The devastation of Cologne, 1945
During World War II, Cologne was a Military Area Command Headquarters (Militärbereichshauptkommandoquartier) for the Military District (Wehrkreis) VI of Münster. Cologne was under the command of Lieutenant-General Freiherr Roeder von Diersburg, who was responsible for military operations in Bonn, Siegburg, Aachen, Jülich, Düren, and Monschau. Cologne was home to the 211th Infantry Regiment and the 26th Artillery Regiment.
The Allies dropped 44,923.2 tons of bombs on the city during World War II, destroying 61% of its built up area. During the Bombing of Cologne in World War II, Cologne endured 262 air raids by the Western Allies, which caused approximately 20,000 civilian casualties and almost completely wiped out the central part of the city. During the night of 31 May 1942, Cologne was the target of "Operation Millennium", the first 1,000 bomber raid by the Royal Air Force in World War II. 1,046 heavy bombers attacked their target with 1,455 tons of explosives, approximately two-thirds of which were incendiary. This raid lasted about 75 minutes, destroyed 600 acres (243 ha) of built-up area (61%), killed 486 civilians and made 59,000 people homeless. The devastation was recorded by Hermann Claasen from 1942 until the end of the war, and presented in his exhibition and book of 1947 Singing in the furnace. Cologne - Remains of an old city 
Cologne was taken by the American First Army in early March, 1945. By the end of the war, the population of Cologne had been reduced by 95 percent. This loss was mainly caused by a massive evacuation of the people to more rural areas. The same happened in many other German cities in the last two years of war. By the end of 1945, however, the population had already recovered to approximately 500,000.
By the end of the war, essentially all of Cologne's pre-war Jewish population of 11,000 had been deported or killed by the Nazis. The six synagogues of the city were destroyed. The synagogue on Roonstraße was rebuilt in 1959.
Post-war Cologne until today
Despite Cologne's status as the largest city in the region, nearby Düsseldorf was chosen as the political capital of the federated state of North Rhine-Westphalia. With Bonn being chosen as the provisional federal capital (provisorische Bundeshauptstadt) and seat of the government of the Federal Republic of Germany (then informally West Germany), Cologne benefited by being sandwiched between two important political centres. The city became–and still is–home to a number of federal agencies and organizations. After reunification in 1990, Berlin was made the capital of Germany.
In 1945 architect and urban planner Rudolf Schwarz called Cologne the "world's greatest heap of rubble". Schwarz designed the master plan for reconstruction in 1947, which included the construction of several new thoroughfares through the city centre, especially the Nord-Süd-Fahrt ("North-South-Drive"). The master plan took into consideration the fact that even shortly after the war a large increase in automobile traffic could be anticipated. Plans for new roads had already, to a certain degree, evolved under the Nazi administration, but the actual construction became easier when most of the city centre was in ruins.
The destruction of 95% of the city centre, including the famous Twelve Romanesque churches such as St. Gereon, Great St. Martin, St. Maria im Kapitol and several other monuments in World War II, meant a tremendous loss of cultural treasures. The rebuilding of those churches and other landmarks such as the Gürzenich event hall was not undisputed among leading architects and art historians at that time, but in most cases, civil intention prevailed. The reconstruction lasted until the 1990s, when the Romanesque church of St. Kunibert was finished.
In 1959, the city's population reached pre-war numbers again. It then grew steadily, exceeding 1 million for about one year from 1975. It remained just below that until mid-2010, when it exceeded 1 million again.
Soviet letter's envelope in honor of the Internationale Philatelic Exhibition LUPOSTA
in Cologne in 1983.
In the 1980s and 1990s Cologne's economy prospered for two main reasons. The first was the growth in the number of media companies, both in the private and public sectors; they are especially catered for in the newly developed Media Park, which creates a strongly visual focal point in Cologne city centre and includes the KölnTurm, one of Cologne's most prominent high-rise buildings. The second was the permanent improvement of the diverse traffic infrastructure, which made Cologne one of the most easily accessible metropolitan areas in Central Europe.
Due to the economic success of the Cologne Trade Fair, the city arranged a large extension to the fair site in 2005. At the same time the original buildings, which date back to the 1920s, were rented out to RTL, Germany's largest private broadcaster, as their new corporate headquarters.
Cologne was the focus of the 2015 New Year's Eve sexual assaults, with over 500 women reporting that they were sexually assaulted by persons of African and Arab appearance.