Mosque of Amr ibn al-As
When the Arab general who conquered Egypt for Islam in 640, Amr ibn al-As, marked the state's first capital at al-Fustat ("the tent" in Arabic, just south of present-day Cairo, near Coptic Cairo at the Mar Girgis Metro stop), he created the first mosque in Egypt, and by extension the first mosque in all of Africa.
The Mosque of Amr ibn al-As, completed in 642, however is not in its original form. It was rebuilt several times in the last 1300 years for a few different reasons.
The population of al-Fustat steadily rose as more Muslims started moving to the new Islamic state of Egypt and less than 30 years after the mosque was completed, it was demoloshied and rebuilt to make room for the people coming to pray. This time however, a tower was added to each side of the mosque -- they weren't known as "minarets" just yet, but they were the first minarets to be built in Islamic history and al-As is the first mosque to introduce the idea of sending a man up higher than the roof to call the adhan (call to prayer) five times a day (Bilal used to stand on the roof in Madinah to call the adhan).
40 years later (around 710), the mosque was expanded yet again. And this time, a mihrab (a recess in the wall that faces Mecca where the imam stands to pray) was added. It was the second mihrab to be found in a mosque, the first being Muhammad's (saw) mosque in Madinah.
And for a final time, in 826, the mosque was rebuilt to its current size today. Marble columns and the many arches that line the interior of al-As were a few of the new additions.
But after a fire in the 12th century and collapses over the years, most recently in 2005, the mosque is hardly in its original state.
Yet there's no denying the beauty of the almost infinite arches leading into this expansive courtyard, centered by the domed drinking fountain. The oldest mosque in Africa and definitely one of Cairo's most beautiful.
Stitched this photo together from 5 frames in Photoshop CS5