There are so many them(=handaxes), all so wonderfully crafted, that I believe they were intended as gifts, as offerings that have come down through all the ages, across all that time.
Could someone explain to me about the tense of "have come down" ?
If this part were expressed like "as offerings that (should) come down" or "as offerings to come down", I could understand much more clearly.
Or, I wonder if the author wanted to imply the fact they(=handaxes) really have come down until now"?
It is a collocation with the meaning that they have survived through the ages until the present. It often is linked to possessions that are passed from one generation to the next: "The pictures in the house have come down to us from our ancestors."
There is no particular connection with "offerings".