Baalbek, known in antiquity as Heliopolis ("Sun City"), is home to some of the best-preserved Roman ruins in Lebanon, many of the structures rivaling those that remain in Rome today. The city was once the center of the solar cult that worshipped the sun as both a natural entity and living god, and temples were also built to the Roman gods Jupiter, Venus, and Bacchus, mirrors of the Canaanite deities Hadad and Atargatis. The temple complex underwent several religious shifts, a testament to Lebanon's diverse yet tumultuous spiritual history: during the Canaanite period, the local temples were largely devoted to the Heliopolitan Triad of the god Baʿal, his consort Ashtart, and their son Adon, while Islamic mythology claimed it as a palace of Solomon's which was put together by djinn and given as a wedding gift to the Queen of Sheba. 

Heliopolis was a noted oracle and pilgrimage site, with inscriptions to the Heliopolitan god discovered in Athens, Rome, Pannonia, Venetia, Gaul, and near the Wall in Britain. Ultimately, the site vied with Praeneste in Italy as the two largest sanctuaries in the Western world. The emperor Trajan consulted the site's oracle twice.

The rise of Christianity introduced a period of religious turmoil in Heliopolis -  early Christian writers such as Eusebius repeatedly denounced the practices of the local pagans, and Constantine demolished the Temple of Venus, raised a basilica in its place, and outlawed the local practice of polygamy. The city was so noted for its hostility to Christians that Alexandrians were banished to it as a special punishment. The Temple of Jupiter, already greatly damaged by earthquakes, was demolished under Theodosius in 379 and replaced by another basilica, using stones scavenged from the pagan complex. He is also said to have been responsible for destroying all the lesser temples and shrines of the city. Under the reign of Justinian, eight of the complex's Corinthian columns were disassembled and shipped to Constantinople for incorporation in the rebuilt Hagia Sophia sometime between 532 and 537. 

In 1516, Baalbek was conquered with the rest of Syria by the Ottoman sultan Selim the Grim. From the 16th century, European tourists began to visit the colossal and picturesque ruins. Donne declared that "No ruins of antiquity have attracted more attention than those of Heliopolis, or been more frequently or accurately measured and described." The Englishman Robert Wood's 1757 Ruins of Balbec included carefully measured engravings that proved influential on British and Continental Neoclassical architects.

The temple complex is located on an immense raised plaza erected 16 ft over an earlier T-shaped base consisting of a podium, staircase, and foundation walls. These walls were built from about 24 monoliths, at their lowest level weighing approximately 330 tons each. The tallest retaining wall, on the west, has a second course of monoliths containing the famous "Three Stones": a row of three stones, each over 62 ft long, 14 ft high, and 12 ft broad, cut from limestone. They weigh approximately 880 tons each. A fourth, still larger stone is called the Stone of the Pregnant Woman: it lies unused in a nearby quarry 2,600 ft from the town. Its weight is estimated at 1,100 tons. A fifth, still larger stone weighing approximately 1,300 tons lies in the same quarry. Three enormous passages the size of railway tunnels run through the foundation.

The Temple of Bacchus may have been completed under Septimius Severus in the 190s, as his coins are the first to show it beside the Temple of Jupiter. It is the best preserved of the sanctuary's structures, as the other rubble from its ruins protected it. The temple is surrounded by forty-two columns—8 along each end and 15 along each side—nearly 66 ft in height.

The Temple of Venus—also known as the Circular Temple or Nymphaeum—was added under Septimius Severus in the early 3rd century but destroyed under Constantine, who raised a basilica in its place.  It lies about 150 yards from the southeast corner of the Temple of Bacchus.