Cairo is the capital city of Egypt. It has population of about 17.285 million people
Cairo is the sixteenth most populous metropolitan area in the world. It is also the most populous metropolitan area in Africa.
Today, Greater Cairo encompasses various historic towns and modern districts into one of the most populous cities in the world. A journey through Cairo is a virtual time travel: from the Pyramids, Saladin's Citadel, the Virgin Mary's Tree, the Sphinx, and ancient Heliopolis, to Al-Azhar, the Mosque of Amr ibn al-A'as, Saqqara, the Hanging Church, and the Cairo Tower. It is the Capital of Egypt, and indeed its history is intertwined with that of the country.

The Islamic Conquest (641 – 969) In AD 640 a Muslim army commanded by the Arabian general Amr ibn al-A'as, laid siege to the Fortress of Babylon near what is today Cairo.He was an Arab military commander who is most noted for leading the Islamic conquest of Egypt in 640. He was a contemporary of Muhammad who rose quickly through the Muslim hierarchy following his conversion to Islam in the year 8 AH (629 CE). He founded the Egyptian capital of Fustat, and built the Mosque of Amr ibn al-As at its center -- the first Mosque on the continent of Africa. It was a matter of time before the Byzantine governor of Egypt agreed to peacefully surrender the fortress, and less than a year later, the capital city Alexandria as recorded in the Treaty of Misr. Amr became the first Arab ruler of Egypt and remained so until his death.
Salah El Din and the Crusades (1168 - 1250)
The last Fatimid Caliph was only eighteen when the Seljuks captured Cairo. The Seljuks who came originally form Central Asia had already conquered Syria and Palestine, and established their capital in Damascus. By 1168, Egypt had become a battleground between the Seljuks and the Crusaders, with the Fatimids having virtually little or no control, although they sided mostly with the Crusaders.

The Mamluks (1250 – 1517)
When Saladin established his rule over Cairo, his Seljuk army was mainly composed of slaves and former slaves who had climbed up the ranks. They were mostly Circassians from the Caucasus region or Central Asians who were captured in military raids or, in most instances, kidnapped by slave merchants. The military power of the male slaves had been on the rise since the early Abbasid rule, but their political influence tremendously increased when Saladin rewarded them extravagantly for their loyalty.

French Expedition (1798 – 1801)
It was in the summer of 1798 that Napoleon's army landed in Alexandria and advanced to Cairo. Murad Bey and Ibrahim Bey, the Mamelouk rulers of Egypt, sent a messenger with a small tribute and asked the French general to leave the country. They had never heard of Napoleon before. The French captured Cairo with little resistance shortly after. It was during their presence that Egypt came out of its long Dark Age.

The era of Muhammad Ali and his successors
Under Muhammad Ali's rule, Cairo prospered both economically and culturally. Not only was the infrastructure of the city rebuilt, but a new city center was also planned according to European standards. During the six-year reign of Muhammad Ali's grandson, Abbas, the first railway line was constructed between Alexandria and Cairo, soon to be followed by a railroad network covering the Delta and Upper Egypt with Cairo at its center.

https://islamstory.com/en/artical/31910