The founding of Rome is shrouded in legend such as the story of Romulus and Remus, but archaeological evidence supports the theory that Rome grew from pastoral settlements on the Palatine Hill and in the area of the future Roman Forum, coalescing into a city in the 8th century BC. That city developed into the capital of the Roman Kingdom (ruled by a succession of seven kings, according to tradition), Roman Republic (from 510 BC, governed by the Senate), and finally the Roman Empire (from 31 BC, ruled by an Emperor); this success depended on military conquest, commercial predominance, as well as selective assimilation of neighboring civilizations, most notably the Etruscans and Greeks. Roman dominance expanded over most of Europe and the shores of the Mediterranean sea, while its population surpassed one million inhabitants. For almost a thousand years, Rome was the most politically important, richest and largest city in the Western world, and remained so after the Empire started to decline and was split, even if it ultimately lost its capital status to Milan and then Ravenna, and was surpassed in prestige by the Eastern capital Constantinople.
With the rise of early Christianity, the Bishop of Rome gained religious as well as political importance, eventually becoming known as the Pope and establishing Rome as the centre of the Catholic Church. After the Sack of Rome (410) by Alaric I and the fall of the Western Roman Empire in 476, Rome alternated between Byzantine rule and plundering by Germanic barbarians. Its population declined to a mere 20,000 during the Early Middle Ages, reducing the sprawling city to groups of inhabited buildings interspersed among large areas of ruins and vegetation. Rome remained nominally part of the Byzantine Empire until 751 when the Lombards finally abolished the Exarchate of Ravenna. In 756, Pepin the Short gave the pope temporal jurisdiction over Rome and surrounding areas, thus creating the Papal States.
Rome remained the capital of the Papal States until its annexation into the Kingdom of Italy in 1870; the city became a major pilgrimage site during the Middle Ages and the focus of struggles between the Papacy and the Holy Roman Empire starting with Charlemagne, who was crowned its first emperor in Rome on Christmas of 800 by Pope Leo III. Apart from brief periods as an independent city during the Middle Ages, Rome kept its status of Papal capital and “holy city” for centuries, even when the Pope briefly relocated to Avignon (1309–1337). While no longer politically powerful, as tragically shown by the brutal sack of 1527, the city flourished as a hub of cultural and artistic activity during the Renaissance and the Baroque, under the patronage of the Papal court. Population rose again and reached 100,000 during the 17th century, but Rome ultimately lagged behind the rest of the European capitals over the subsequent centuries, being largely busy in the Counter-Reformation process.
Caught up in the nationalistic turmoil’s of the 19th century and having twice gained and lost a short-lived independence, Rome became the focus of the hopes for Italian unification, as propelled by the Kingdom of Italy ruled by King Vittorio Emanuele II; after the French protection was lifted in 1870, royal troops stormed the city, and Rome was declared capital of the newly unified Italy in 1871. After a victorious World War I, Rome witnessed the rise to power of Italian fascism guided by Benito Mussolini, who marched on the city in 1922, eventually declared a new Empire and allied Italy with Nazi Germany. This was a period of rapid growth in population, from the 212,000 people at the time of unification to more than 1,000,000, but this trend was halted by World War II, during which Rome was damaged by both Allied forces bombing and Nazi occupation; after the execution of Mussolini and the end of the war, a 1946 referendum abolished the monarchy in favor of the Italian Republic.
Rome grew momentously after the war, as one of the driving forces behind the “Italian economic miracle” of post-war reconstruction and modernization. It became a fashionable city in the 1950s and early 1960s, the years of “‘la Dolce Vita'” (“the sweet life”), and a new rising trend in population continued till the mid-1980s, when the commune had more than 2,800,000 residents; after that, population started to slowly decline as more residents moved to nearby comunities; this has been attributed to their perceiving a decrease in the quality of life, especially because of the continuously jammed traffic and the worsening pollution it brings about.