As a time-travelling SG-1 sees firsthand in the two-part episode Moebius, Ra reigned in Ancient Egypt around 3000 B.C. During that time, Ra used Goa'uld technology, and the human resistance gathered hundreds of staff weapons and other Goa'uld technology to drive Ra away.
The novel Moebius Squared revisits this era and shows that three years after the rebellion, the humans did not destroy their staff weapons and zat guns, and they use them again.
Given this, why is it that so few artifacts from Goa'uld reign exist for modern archaeologists to find? All they found is the Stargate, the DHD that the Nazis eventually got a hold of, and a number of religious artifacts from Ra and other "gods". Why aren't they finding staff weapons, dead Jaffa armor, and other stuff from the Goa'uld reign?