[2] During the Roman period, beginning after the fall of Jerusalem in the year 70, the entire region (Judea, Samaria, and the Galilee) was renamed Palaestina, subdivided into Diocese I and II.

[4] During the last of the Roman-Persian Wars, beginning in 603, the Persians under Khosrau II had succeeded in occupying Syria, Palestine and Egypt for over a decade before being forced by the victories of Heraclius to conclude the peace of 628.

[5] Politically, the Syrian region consisted of two provinces: Syria proper stretched from Antioch and Aleppo in the north to the top of the Dead Sea.

The Byzantine Emperor Heraclius, after re-capturing Syria from the Sassanians, set up new defense lines from Gaza to the south end of the Dead Sea.

These lines were only designed to protect communications from bandits, and the bulk of the Byzantine defenses were concentrated in Northern Syria facing the traditional foes, the Sassanid Persians.

The drawback of this defense line was that it enabled the Muslims, advancing from the desert in the south, to reach as far north as Gaza before meeting regular Byzantine troops.

After the Farewell Pilgrimage in 632, Muhammad appointed Usama ibn Zayd as the commander of an expeditionary force which was to invade the region of Balqa in the Byzantine Empire.

As the main Byzantine defence line started from the coastal regions near Ghazahh,[dubious – discuss] Yazid arrived at the Valley of Araba at about the same time as Amr bin Al Aas reached Elat.

The combined forces of Khalid, Shurhabil, and Abu Ubaidah then resumed the siege of Bosra, which surrendered some time in mid-July 634 CE, effectively ending the Ghassanid Dynasty.

After three days, Khalid took a cavalry force, caught up to the Romans using an unknown shortcut, and attacked them at the Battle of Maraj-al-Debaj, 305 kilometres (190 miles) north of Damascus.

[18] Soon after the appointment of Abu-Ubaidah as commander in chief, he sent a small detachment to the annual fair held at Abu-al-Quds, modern day Ablah, near Zahlé 50 kilometres (31 miles) east of Beirut.

Khalid reached the battlefield and defeated the garrison on 15 October and returned with tons of looted booty from the fair and hundreds of Roman prisoners.

Abu Ubaidah decided to march to Fahl, which is about 150 metres (500 ft) below sea level, where a strong Byzantine garrison and survivors of the Battle of Ajnadayn were present.

Umar, after having learned of the position and strength of the Byzantine army in Palestine, wrote detailed instructions to his corps commanders there and ordered Yazid to capture the Mediterranean coast.

According to lexicographer David ben Abraham al-Fasi (died before 1026 CE), the Muslim conquest of Palestine brought relief to the country's Jewish citizens, who had previously been barred by the Byzantines from praying on the Temple Mount.

In the meantime, the Byzantine army split in two, one deployed at Maraj al Rome (Beqaa Valley) led by Schinos; the other, commanded by Theodras, stationed to the west of Damascus (Al-Sabboura region).

Abu Ubaidah accepted the offer and, rather than invading districts of Emesa and Chalcis, he consolidated his rule in conquered land and captured Hamah, and Maarrat al-Nu'man.

The prisoners were interrogated and informed him about Emperor Heraclius' ambitious plan to take back Syria with an army possibly two hundred thousand (200,000) strong.

From Jabiya, again on Khalid's suggestion, Abu Ubaidah ordered the Muslim troops to withdraw to the Plain of the Yarmouk River, where the cavalry could be used effectively.

While the Muslim armies were gathering at Yarmouk, Khalid intercepted and routed the Byzantine advance guard, ensuring a safe path of retreat.

[citation needed] Yazdegerd III lost his army at the Battle of Qadisiyyah in November, three months after Yarmouk, ending Sassanid control west of Persia.

Menas, diverting from conventional Byzantine tactics, decided to face Khalid and destroy the leading elements of Muslim army before the main body could join them at Hazir 5 kilometres (3 mi) east of Chalcis.

Khalid and Abu Ubaidah continued their march northward and laid siege to Aleppo, which was captured after fierce resistance from desperate Byzantine troops in October.

They accordingly sent detachments north to eliminate all possible Byzantine forces and captured the garrison town of Azaz, 50 kilometres (30 mi) from Aleppo; from there Muslims attacked Antioch from the eastern side, resulting in the Battle of Iron bridge.

Abu Ubaidah sent Khalid towards the north and he himself marched to the south and captured Tartus, Jablah, and finally Latakia and the coastal areas west of the Anti-Lebanon Mountains.

He thus sought help from the Christians (some of whom were Arabs) of Jazirah, mainly from Circesium and Hīt, who mustered a large army and marched against Emesa, Abu Ubaidah's headquarters.

Khalid was in favor of an open battle outside the fort, but Abu Ubaidah referred the matter to Umar, who sent a detachment from Iraq to invade Jazirah from three different routes.

In 639–640, Raqqa fell into Muslim hands,[29] followed by most of Jazirah, the last base of the Eastern Roman Empire in the region, which surrendered peacefully and agreed to pay Jizya.

In 645–646, Sufyan bin Mujib Al-Azdi, appointed by Muawiyah, managed to seize Tripoli to eventually capture the last Byzantine stronghold on the Levantine coast.

The Byzantine civil service was retained until a new system could be instituted; therefore, Greek remained the administrative language in the new Muslim territories for over 50 years after the conquests.