Herodotus, book 4, ch.62 : This is their way of sacrificing to other gods and these are the beasts offered; but their sacrifices to Ares are of this sort. Every district in each of the governments has a structure sacred to Ares; namely, a pile of bundles of sticks three eighths of a mile wide and long, but of a lesser height, on the top of which there is a flattened four-sided surface; three of its sides are sheer, but the fourth can be ascended. Every year a hundred and fifty wagon-loads of sticks are heaped upon this; for the storms of winter always make it sink down. On this sacred pile an ancient scimitar of iron is set for each people: their image of Ares. They bring yearly sacrifice of sheep and goats and horses to this scimitar, offering to these symbols even more than they do to the other gods. Of enemies that they take alive, they sacrifice one man in every hundred, not as they sacrifice sheep and goats, but differently. They pour wine on the men's heads and cut their throats over a bowl; then they carry the blood up on to the pile of sticks and pour it on the scimitar. They carry the blood up above, but down below by the sacred pile they cut off all the slain men's right arms and hands and throw these into the air, and depart when they have sacrificed the rest of the victims; the arm lies where it has fallen, and the body apart from it.
Archaeological evidence: https://www.academia.edu/11582741/Scythian_sanctuaries_of_Ares_archaeological_date_and_Herodotus_testimonies_in_English_