Excerpts from Books and Wikipedia
"IN 670, TWO YEARS AFTER Constantine IV’s accession, the Arab advance along the North African coast began again. At the same time, the Arab spread continued to the east. In the mountains north of India, Arab armies drove the king of the Shahi out of Kabul, his capital;* the Shahi kingdom kept control of the Khyber Pass but was forced to move its capital city east to Udabhandapura. The multipronged expansion reached Constantinople in 674, when Arab armies laid siege to the city itself. The siege lasted four years, but Constantinople was able to continually refresh its supplies by sea, and conditions never became desperate. The Arab navy launched a final sea attack in 678, but the Byzantine ships made use of their famous “Greek fire,” a chemical concoction launched through tubes that kept burning even when it met the water, and finally the Arab ships withdrew—followed shortly after by the land forces." [Bauer: Medieval World, p. 321]