Back when I was a young nerd... I majored in Medieval Studies at the University of California. I had a set of these books.
Not the originals, of course, but a student budget version. I read them. Very, very carefully.
Volume 5 is particularly interesting. It begins thusly:
While the state was exhausted by the Persian war, and the church was distracted... Mahomet, with the sword in one hand and the Koran in the other, erected his throne on the ruins of Christianity and of Rome.
The genius of the Arabian prophet, the manners of his nation, and the spirit of his religion, involve the causes of the decline and fall of the Eastern empire; and our eyes are curiously intent on one of the most memorable revolutions, which have impressed a new and lasting character on the nations of the globe.
You don't have to overload your UPS man or short out the Kindle in order to glean the benefits of Gibbons' insights. Read the text online. It is most fascinating.