Heliopolis, the City of the Sun
The city retained its religious function during Roman times, when the sanctuary of the Heliopolitan Jupiter-Baal was a pilgrimage site. Trajan's biographer records that the Emperor consulted the oracle there. Trajan inquired of the Heliopolitan Jupiter whether he would return alive from his wars against the Parthians. In reply, the god presented him with a vine shoot cut into pieces. Theodosius Macrobius, a Latin grammarian of the 5th century AD, mentioned Zeus Heliopolitanus and the temple, a place of oracular divination. Starting in the last quarter of the 1st century BC and over a period of two centuries, the Romans had built a temple complex in Baalbeck consisting of three temples: Jupiter, Bacchus and Venus. On a nearby hill, they built a fourth temple dedicated to Mercury.
The city, then known as Heliopolis (there was another Heliopolis in Egypt), was made a colonia by the Roman Empire in 15 BC and a legion was stationed there. Work on the religious complex there lasted over a century and a half and was never completed. The dedication of the present temple ruins, the largest religious building in the entire Roman empire, dates from the reign of Septimus Severus, whose coins first show the two temples. The great courts of approach were not finished before the reigns of Caracalla and Philip. In commemoration, no doubt, of the dedication of the new sanctuaries, Severus conferred the rights of the ius Italicum on the city. Today, only six Corinthian columns remain standing. Eight more were disassembled and shipped to Constantinople under Justinian's orders, for his basilica of Hagia Sophia.
The greatest of the three temples was sacred to Jupiter Baal, ("Heliopolitan Zeus"), identified here with the sun, and - constructed between the first century BC and 62 AD - was the largest temple in the empire. With it were associated a temple to Venus and a lesser temple in honor of Bacchus (though it was traditionally referred to as the "Temple of the Sun" by Neoclassical visitors, who saw it as the best-preserved Roman temple in the world - it is surrounded by forty-two columns nearly 20 meters in height). Thus three Eastern deities were worshipped in Roman guise: thundering Jove, the god of storms, stood in for Baal-Hadad, Venus for ‘Ashtart (known in English as Astarte) and Bacchus for Anatolian Dionysus.
The Roman construction was built on top of earlier ruins and involved the creation of an immense raised plaza onto which the actual buildings were placed. The sloping terrain necessitated the creation of retaining walls on the north, south and west sides of the plaza. These walls are built of monoliths at their lowest level each weighing approximately 400 tons. The western, tallest retaining wall has a second course of monoliths containg the famous "trilithon"; a row of three stones each weighing in excess of 1000 tons. A fourth, still larger stone called "the stone of the south" (Hajar el Gouble) or "the stone of the pregnant woman" (Hajar el Hibla) lays unused in a nearby quarry. Had it been freed from the quarry, it would have been the largest stone ever moved, larger than the famous unfinished obelisk in Aswan. Another of the Roman ruins, the Great Court, has six 20 m-tall stone columns surviving, out of an original 128.
Jupiter-Baal was represented locally (on coinage) as a beardless god in long scaly drapery, holding a whip in his right hand and thunderbolts and ears of wheat in his left. Two bulls supported him. In this guise he passed into European worship in the 3rd century and 4th century AD. The icon of Helipolitan Zeus (in A.B. Cook, Zeus, i:570-576) bore busts of the seven planetary powers on the front of the pillarlike term in which he was encased. A bronze statuette of this Heliopolitan Zeus was discovered at Tortosa, Spain; another was found at Byblos in Phoenicia. A comparable iconic image is the Lady of Ephesus (see illustration) (Robert Graves, The Greek Myths I.4).
Other Emperors enriched the sanctuary of Heliopolitan Jupiter each in turn. Nero (54-68 AD) built the tower-altar opposite the Temple of Jupiter, Trajan added the forecourt to the Temple of Jupiter, with porticos of pink granite brought from Aswan in Egypt. Antoninus Pius built the Temple of Bacchus, the best preserved of the sanctuary's structures, for it was protected by the very rubble of the site's ruins. It is enriched with refined reliefs and sculpture. Septimus Severus added a pentagonal Temple of Venus, who as Aphrodite had enjoyed an early Syrian role with her consort Adonis ("Lord", the Aramaic translation of "Baal."). Christian writers competed with one another to execrate her worship. Eusebius of Caesarea, down the coast, averred that 'men and women vie with one another to honour their shameless goddess; husbands and fathers let their wives and daughters publicly prostitute themselves to please Astarte'. Emperor Philip the Arab (244-249) was the last to add a monument at Heliopolis— the hexagonal forecourt. When he was finished Heliopolis and Praeneste in Italy were the two largest sanctuaries in the Western world.
The extreme licence of the Heliopolitan worship of Aphrodite was often commented upon by early Christian writers, and Constantine, making an effort to curb the Venus cult, built a basilica. Theodosius I erected another, with a western apse, occupying the main court of the Jupiter temple, as was Christian practice everywhere. The vast stone blocks of its walls were taken from the temple itself. Today nothing of the Theodosian basilica remains.
 Early Islamic period
In 637 A.D Muslim army under Abu Ubaida ibn al-Jarrah captured Baalbek after defeating the Byzantine army at Battle of Yarmouk, it was still an opulent city and yielded rich booty. It became a bone of contention between the various Syrian dynasties and the caliphs first of Damascus, then of Egypt. The place was fortified and took on the name al-Qala‘ ("fortress"; see Alcala) but in 748 was sacked again with great slaughter. The Byzantine emperor John Tzimisces sacked the city in 975. In 1090 it passed to the Seljuks and in 1134 to Zengi; but after 1145 it remained attached to Damascus and was captured by Saladin in 1175. The Crusaders raided its valley more than once, but never took the city. Three times shaken by earthquakes in the 12th century, it was dismantled by 1260. But it revived, and most of its fine mosque and fortress architecture, still extant, belongs to the reign of Sultan Qalawun (1282) and the succeeding century, during which Abulfeda describes it as a very strong place. In 1400 Timur pillaged it.
 Ottoman period
In 1517 it passed, with the rest of Syria, to the Ottoman Empire. But Ottoman jurisdiction was merely nominal in the Lebanon. Baalbeck, badly shaken in an earthquake in 1759 was really in the hands of the Metawali (see Lebanon), who retained it against other Lebanese tribes. The colossal and picturesque ruins attracted particularly intrepid Westerners since the 18th century. The English visitor, Robert Wood, with Dawson was not simply a tourist: his carefully measured drawings were engraved for The Ruins of Baalbeck (1757), which provided some excellent new detail in the Corinthian order that British and European Neoclassical architects added to their vocabulary. Robert Adam, for example, based a bed and one of the ceilings at Osterley House on the ceiling of the Temple of Bacchus, and the portico of St George's, Bloomsbury is based on that temple's portico.
Even after Jezzar Pasha, the rebel governor of Acre province, broke the power of the Metawali in the last half of the 18th century, Baalbeck was no destination for the traveller unaccompanied by an armed guard. The anarchy that succeeded his death in 1804 was ended only by the Egyptian occupation (1832). With the treaty of London (1840) Baalbeck became really Ottoman, the Encyclopaedia Britannica (1911) reported, and since about 1864 had attracted great numbers of tourists. In November 1898, the German Emperor Wilhelm II on his way to Jerusalem, and passing by Baalbeck was equally struck by the magnificence of the ruins projecting from the rubble, and the dreary condition. Within a month, the German archaeological team he dispatched was at work on the site. The campaign produced meticulously presented and illustrated series of volumes.
 World Heritage Site
"Baalbeck, with its colossal structures, is one of the finest examples of Imperial Roman architecture at its apogee", UNESCO reported in making Baalbek a World Heritage Site in 1984. When the Committee inscribed the site, it expressed the wish that the protected area include the entire town within the Arab walls, as well as the south-western extramural quarter between Bastan-al-Khan, the Roman site and the Mameluk mosque of Ras-al-Ain. Lebanon's representative gave assurances that the Committee's wish would be honored.
 Israel-Lebanon conflict
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Baalbeck, which has a Shiite majority, is considered for years as Hezbollah's "strategic headquarter" and some of the organization's commanders live in it. It is housing also a hospital which serves the Hezbollah and an Islamic college. According to the Hezbollah, the team that kidnapped the two Israeli soldiers on July 13th, 2006, and brought Israel to declare war, trained in Baalbeck region. 
On August 2, 2006, Israeli helicopter-borne soldiers supported by bombs from aircraft entered the Hikmeh Hospital in Baalbeck to capture senior members of Hezbollah who they believed to be in the building. The result of fighting between the fighters and Israeli forces was minor damage to the hospital. Several gunmen were killed and weapons and ammunition were seized from inside the hospital building. No patients were hospitalized at the time. It has been reported that during the conflict, vibrations caused by bombs damaged the ruins; UNESCO was to help coordinate restoration efforts.
Templo de Baco, reconstrucción