The last century of Seleucid rule was marked by disorder and dynastic struggles.
These ended in 64 BC, when the Roman general Pompey added Seleucid Syria and Lebanon as a Roman province to the Roman Empire.
Economic and intellectual activities flourished in Lebanon during the Pax Romana.
The inhabitants of the principal Phoenician cities of Byblos, Sidon, and Tyre were granted Roman citizenship.
These cities were centers of the pottery, glass, and purple dye industries; their harbors also served as warehouses for products imported from Syria, Persia, and India.
They exported cedar, perfume, jewelry, wine, and fruit to Rome.
Economic prosperity led to a revival in construction and urban development; temples and palaces were built throughout the country, as well as paved roads that linked the main cities like Heliopolis and Berytus.

Indeed, starting in the last quarter of the 1st century BCE (reign of Augustus)  and over a period of two centuries (reign of Philip the Arab), the Romans built a huge temple complex in Heliopolis (actual Baalbek) on a pre-existing tell consisting of three temples: Jupiter, Bacchus and Venus.
On a nearby hill, they built a fourth temple dedicated to Mercury.

Furthermore, the veterans of two Roman legions were established in the city of Berytus (actual Beirut): the fifth Macedonian and the third Gallic.
The city quickly became Romanized.
Large public buildings and monuments were erected and Berytus enjoyed full status as a part of the empire.

Under the Romans, Berytus was enriched by the dynasty of Herod the Great, and was made a colonia, Colonia Iulia Augusta Felix Berytus, in 14 BC.
Beirut's school of law was widely known at the time.
Two of Rome's most famous jurists, Papinian and Ulpian, both natives of Phoenicia, taught at the law school under the Severan emperors.

Furthermore, The city of Heliopolis was made a colonia by Septimius Severus in 193 AD, having been part of the territory of Berytus on the Phoenician coast since 15 BC.
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 (211-217 CE) and Philip the Arab (244-249 CE).
In commemoration 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 of this huge Jupiter temple.

Severus also separated the area of modern Lebanon and parts of Syria from the greater province of Syria Coele, and formed the new province of Phoenice.

Upon the death of Theodosius I in 395 AD, the empire was divided in two: the eastern or Byzantine part with its capital at Constantinople, and the western part with its capital at Rome.
Under the Byzantine Empire, intellectual and economic activities in Beirut, Tyre, and Sidon continued to flourish for more than a century.
However, in the 6th century a series of earthquakes demolished the temples of Heliopolis and destroyed the Romanized city of Beirut, leveling its famous law school and killing nearly 30,000 inhabitants.
To these natural disasters were added the abuses and corruptions prevailing at that time in the empire.
Heavy tributes and religious dissension produced disorder and confusion.
Furthermore, the ecumenical councils of the 5th and 6th centuries were unsuccessful in settling religious disagreements.
This turbulent period weakened the empire and made it easy prey to the newly converted Muslim Arabs of the Arabian Peninsula.
The last century of Seleucid rule was marked by disorder and dynastic struggles. These ended in 64 BC, when the Roman general Pompey added Seleucid Syria and Lebanon as a Roman province to the Roman Empire. Economic and intellectual activities flourished in Lebanon during the Pax Romana. The inhabitants of the principal Phoenician cities of Byblos, Sidon, and Tyre were granted Roman citizenship. These cities were centers of the pottery, glass, and purple dye industries; their harbors also served as warehouses for products imported from Syria, Persia, and India. They exported cedar, perfume, jewelry, wine, and fruit to Rome. Economic prosperity led to a revival in construction and urban development; temples and palaces were built throughout the country, as well as paved roads that linked the main cities like Heliopolis and Berytus. 
Indeed, starting in the last quarter of the 1st century BCE (reign of Augustus)  and over a period of two centuries (reign of Philip the Arab), the Romans built a huge temple complex in Heliopolis (actual Baalbek) on a pre-existing tell consisting of three temples: Jupiter, Bacchus and Venus. On a nearby hill, they built a fourth temple dedicated to Mercury.
Furthermore, the veterans of two Roman legions were established in the city of Berytus (actual Beirut): the fifth Macedonian and the third Gallic. The city quickly became Romanized. Large public buildings and monuments were erected and Berytus enjoyed full status as a part of the empire.
Under the Romans, Berytus was enriched by the dynasty of Herod the Great, and was made a colonia, Colonia Iulia Augusta Felix Berytus, in 14 BC. Beirut's school of law was widely known at the time. Two of Rome's most famous jurists, Papinian and Ulpian, both natives of Phoenicia, taught at the law school under the Severan emperors. 
Furthermore, The city of Heliopolis was made a colonia by Septimius Severus in 193 AD, having been part of the territory of Berytus on the Phoenician coast since 15 BC. 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 (211-217 CE) and Philip the Arab (244-249 CE). In commemoration 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 of this huge Jupiter temple.
Severus also separated the area of modern Lebanon and parts of Syria from the greater province of Syria Coele, and formed the new province of Phoenice.
Upon the death of Theodosius I in 395 AD, the empire was divided in two: the eastern or Byzantine part with its capital at Constantinople, and the western part with its capital at Rome. Under the Byzantine Empire, intellectual and economic activities in Beirut, Tyre, and Sidon continued to flourish for more than a century. However, in the 6th century a series of earthquakes demolished the temples of Heliopolis and destroyed the Romanized city of Beirut, leveling its famous law school and killing nearly 30,000 inhabitants. To these natural disasters were added the abuses and corruptions prevailing at that time in the empire. Heavy tributes and religious dissension produced disorder and confusion. Furthermore, the ecumenical councils of the 5th and 6th centuries were unsuccessful in settling religious disagreements. This turbulent period weakened the empire and made it easy prey to the newly converted Muslim Arabs of the Arabian Peninsula.
History of ancient Lebanon