now however was the guard of the hills maintained rather by custom than necessity , for the gondothlim had long ago with unimagined toil levelled and cleared and delved all that plain about amon gwareth , so that scarce gnome or bird or beast or snake could approach but was espied from many leagues off , for among the gondothlim were many whose eyes were keener than the very hawks of manwe sulimo lord of gods and elves who dwells upon taniquetil ; and for this reason did they call that vale tumladin or the valley of smoothness .