Why is Rome the holy city?
Several historical factors brought this designation into being.
During the time of Our Lord and the Apostolic Era, Rome was the capital of the Roman Empire and there exist at that time a certain peace in the world known as the Pax Romana. In a sense, the world almost seemed to Rome’s.
The Pax Romana (Latin for "Roman Peace") is a roughly 200-year-long timespan of Roman history which is identified as a period and as a golden age of increased as well as sustained Roman imperialism, relative peace and order, prosperous stability, hegemonial power and regional expansion, despite a number of revolts and wars, and continuing competition with Parthia. It is traditionally dated as commencing from the accession of Caesar Augustus, founder of the Roman principate, in 27 BC and concluding in 180 AD with the death of Marcus Aurelius, the last of the "Five Good Emperors". Since it was inaugurated by Augustus with the end of the Final War of the Roman Republic, it is sometimes called the Pax Augusta. During this period of about two centuries, the Roman Empire achieved its greatest territorial extent and its population reached a maximum of up to 70 million people. According to Cassius Dio, the dictatorial reign of Commodus, later followed by the Year of the Five Emperors and the crisis of the third century, marked the descent "from a kingdom of gold to one of iron and rust".
The expansion of Roman influence lead the Romans into calling the Mediterranean Sea, the Mare Nostrum!
Mare Nostrum (Latin for “Our Sea”) was a common Roman name for the Mediterranean Sea. The term was always somewhat ambiguous: it both implied Roman dominance of the Mediterranean and the cultural diversity of the nations that have bordered it for well over two millennia. Since before the Roman times, the Mediterranean Sea always was a meeting ground for cultures that bordered it–sometimes peaceful, sometimes not.
But the greatest forerunner of calling Rome the Holy City came about in 1st century BC, under Albius Tibullus who called Rome the Eternal City! A designation that is still heard of today, as well as Rome the Holy City.
Rome was called the Eternal City by the poet Albius Tibullus who lived in 55-19 BC. In his poetic work (elegias), the author through Apollo conveys to the readers the idea that Rome will be a powerful city and calls it Urbs Aeterna, or Eternal City: "Not yet had Romulus drawn up the Eternal City’s walls, where Remus as co-ruler was fated not to live". Thus, Tibullus was responsible for starting the trend among people of thinking of their city as the pinnacle of society.
Many Roman speakers and writers began to use the name Eternal City in their writings and speeches. To better understand why Rome was called the Eternal City, it might be helpful to learn about some historical facts of that time. Tibullus lived during the reign of Octavian Augustus. Under this emperor, the city structures, that had been lost earlier, were reconstructed and restored. The emperor proudly declared that he had found the city brick, but left it marble. History has confirmed those words about eternity. Despite the wars, all kinds of upheavals, riots, the city has been rebuilding and strengthening its power. - Who Said That Rome Is Eternal?
Christian Influences for designating Rome as the Holy City.
The Christian factors towards this designation are multiple and start with the foundation of the See of St. Peter and the tomb or St. Peter as a place of pilgrimage as well as that of other countless martyrs buried in the catacombs.
The significance of Rome lies primarily in the fact that it is the city of the pope. The Bishop of Rome, as the successor of St. Peter, is the Vicar of Christ on earth and the visible head of the Catholic Church. Rome is consequently the centre of unity in belief, the source of ecclesiastical jurisdiction and the seat of the supreme authority which can bind by its enactments the faithful throughout the world. The Diocese of Rome is known as the "See of Peter", the "Apostolic See", the "Holy Roman Church" the "Holy See" — titles which indicate its unique position in Christendom and suggest the origin of its preeminence. Rome, more than any other city, bears witness both to the past splendour of the pagan world and to the triumph of Christianity. It is here that the history of the Church can be traced from the earliest days, from the humble beginnings in the Catacombs to the majestic ritual of St. Peter's. At every turn one comes upon places hallowed by the deaths of the martyrs, the lives of innumerable saints, the memories of wise and holy pontiffs. From Rome the bearers of the Gospel message went out to the peoples of Europe and eventually to the uttermost ends of the earth. To Rome, again, in every age countless pilgrims have thronged from all the nations, and especially from English-speaking countries. With religion the missionaries carried the best elements of ancient culture and civilization which Rome had preserved amid all the vicissitudes of barbaric invasion. To these treasures of antiquity have been added the productions of a nobler art inspired by higher ideals, that have filled Rome with masterpieces in architecture, painting, and sculpture. These appeal indeed to every mind endowed with artistic perception; but their full meaning only the Catholic believer can appreciate, because he alone, in his deepest thought and feeling, is at one with the spirit that pulsates here in the heart of the Christian world.
Rome as of today remains one of the greatest pilgrimage locations in the Catholic world. This was compounded during those centuries where the faithful were unable to go on pilgrimage to the Holy Lands to honour those places hollowed by Our Lord, Our Lady and various other locations sanctified by the traditions handed down from the Old Testament.
Even today, all Catholic bishops must come to Rome every five (5) years (more or less) amongst other things: To pray at the tombs of St. Peter and St. Paul. (In addition, they meet with Pope Francis and Vatican officials.)
The *visit ad limina means, technically, the obligation incumbent on certain members of the hierarchy of visiting, at stated times, the "thresholds of the Apostles", Sts. Peter and Paul, and of presenting themselves before the pope to give an account of the state of their dioceses. The object of the visit is not merely to make a pilgrimage to the tombs of the apostles, but, above all, to show the proper reverence for the Successor of St. Peter, to acknowledge practically his universal jurisdiction by giving an account of the condition of particular churches, to receive his admonitions and counsels, and thus bind more closely the members of the Church to its Divinely appointed head. - Visit ad Limina