Today there are great bridges that fill us with wonder by its length: the Akashi-Kaikyo with 1991 mts. in Japan, or the Great Belt East with 1624mts. in Denmark, or Runyang with 1490 mts. in China. They are the world’s largest cable-stayed bridges. In ancient times the Romans were great builders of bridges.
Every great city is bathed by a great river crossed by many bridges as an expression of their power. Rome is one such example. Its river, essential in its history, is the Tiber. It must have been very important the first bridge, the Pons Sublicius, from the time of King Ancus Marcius, built entirely of wood with wooden instruments, because a taboo prevented contact with metal instruments.
So important and need it should be the help of the gods that the highest Roman religious authority was called "Pontifex Maximus" (the maker of the bridge) as the traditional explanation of the term that gives Varro, who also suggests another: from posse and facere (which can make ..); there is one who explains that the name comes from being a bridge of communication between the gods of heaven and mortal men. Certainly the Pope of the Catholic Church holds officially this title because so assumed when the pagan religion disappeared and the Christian religion was imposed as the official religion. The disappearance then was not complete or radical.
In Rome were numerous bridges: Bridge Aemilius, now broken, the Fabricius and Cestius on Tiber Island (small island in the middle of the river); Agrippa’s Bridge, Caligula’s Bridge , Nero's, the Triumphal Bridge , the famous Bridge Aelius or of Hadrian , now known as Ponte Sant'Angelo, the equally famous Milvian Bridge where the confrontation took place between Maxentius and Constantine when he had the vision of the Cross with the words "in hoc signo vinces" (with this sign conquer), etc..
Also Roman bridges, defying the passage of time, are scattered along the all roads of the Roman Empire leading to Rome, to the city, city par excellence. They are not as long as modern, but they have lasted much longer time.
Well, in ancient times there was a project, an idea better, because it did not project, to unite southern Italy to northern Greece with a great bridge. Pliny the Elder says that to us in his encyclopedia Naturalis Historia, III, (XI) 100 et seq. describing Italy:
The towns inland from Tarentum are Varia (modern Oria) surnamed Apulia, Messapia (Mesagna), and Aletium (Santa Maria dell' Alizza); on the coast, Senum, and Callipolis (Gallipoli), now known as Anxa, 75 miles from Tarentum. Thence, at a distance of 32 miles, is the Promontory of Acra Iapygia (Capo di Santa Maria di Leuca) , at which point Italy projects the greatest distance into the sea. At a distance of 19 miles from this point is the town of Basta ( Vaste) , and then Hydruntum (Otranto), the spot at which the Ionian is separated from the Adriatic sea, and from which the distance across to Greece is the shortest. The town of the Apolloniates (Pallina or Pollona) lies opposite to it, and the breadth of the arm of the sea which runs between is not more than fifty miles. Pyrrhus, king of Epirus, was the first who entertained the notion of uniting these two points and making a passage on foot, by throwing a bridge across, and after him M. Varro, when commanding the fleet of Pompey in the war against the Pirates. Other cares however prevented either of them from accomplishing this design. (John Bostock, M.D., F.R.S., H.T. Riley, Esq., B.A., Ed.)
Oppida per continentem a Tarento Uria, cui cognomen ob Apulam Messapiae , Aletium, in ora vero Senum, Callipolis, quae nunc est Anxa, LXXV a Tarento. inde XXXIII promunturium quod Acran Iapygiam vocant, quo longissime in maria excurrit Italia. ab eo Basta oppidum et Hydruntum decem ac novem milia passuum, ad discrimen Ionii et Hadriatici maris, qua in Graeciam brevissimus transitus, ex adverso Apolloniatum oppidi latitudine intercurrentis freti L non amplius. hoc intervallum pedestri continuare transitu pontibus iactis primum Pyrrus Epiri rex cogitavit, post eum M. Varro, cum classibus Pompei piratico bello praeesset; utrumque aliae inpedivere curae
Hydruntum is Otranto in Magna Graecia, Italy; Apollonia is in the ancient Illyria. Since these cities are going to Greece and vice versa and also to Dyrrachium further north. For example Cicero tells us in book XVI,(Epistulae Ad familiares): Epistula 9 ad Tironem :
On the 16th we continued our voyage to Cassiope, a harbour of Corcyra, a distance of 120 stades. There we were detained by winds until the 22nd. Many of those who in this interval impatiently attempted the crossing suffered shipwreck. On the 22nd, after dinner, we weighed anchor. Thence with a very gentle south wind and a clear sky, in the course of that night and the next day we arrived in hìgh spirits on Italian soil at Hydrus, 1 and with the same wind next day—that is, the 24th of November—at 10 o'clock in the morning we reached Brundisium, and exactly at the same time as ourselves Terentia (who values you very highly) made her entrance into the town. (Evelyn Shuckburgh, Ed.)
a.d. xv K. in portum Corcyraeorum ad Cassiopen stadia cxx processimus. ibi retenti ventis sumus usque ad a. d. viiii K. interea, qui cupide profecti sunt, multi naufragia fecerunt.  nos eo die cenati solvimus ; inde austro lenissimo caelo sereno nocte illa et die postero in Italiam ad Hydruntem ludibundi pervenimus eodemque vento postridie (id erat a. d. vii K. Dec.) hora iiii Brundisium venimus, eodemque tempore simul nobiscum in oppidum introiit Terentia, quae te facit plurimi.
Note: Tiro is the famous slave of Cicero, then manumitted, who served as private secretary, writing and reviewing the speaker's speeches with tironianae notae, called Tironian notes, kind of shorthand writing used by the monks to the Middle Ages. Tiro is sometimes called the "Father of shorthand writing." He was also editor of the works of Cicero.
For a time Apolloniates was domain of Pyrrhus, king of Epirus, (most famous for his victory in the way, defeat in the background). Pyrrhus was not only a king who was in check the mighty Rome for a long time, but had great ideas and dreams like this to build a bridge from the shores of Italy to Greece.
Idea that Varro collected when commanded Pompey's fleet against the pirates of the Adriatic. Friend of Cicero, wrote many works of various subjects, but only is completely preserved his De rerum rusticarum (About the field stuff), is incomplete De lingua latina and some remain fragments of other works.
According to Pliny, the war prevented both to realize the dream. The truth is that the war has consumed and consumed countless time and resources that should be devoted to other tasks, such as building bridges. Even the war goes beyond, in their desire to destroy´, the first thing that usually destroyed in the siege or occupation of a territory are precisely the bridges.
Otherwise there were in antiquity similar grandiose projects such as a bridge joining Calabria with Sicily. With this bridge dreamed the Romans (even a pontoon bridge), then Charlemagne and the Normans in the eleventh century and Roger II in the XII and permanently until today they are still dreaming. Now the problem seems to be opposition from environmental lobbyists (read mafia).
The Romans had many wars and few technical resources. Today there are resources, but what seems to be missing is the decision or political courage to carry out this ancient project.