Breaking my rule of 'always avoid alliteration', how about:

-Passionately preserving the past
-Passionately preserving prehistory
-Our passion is preserving prehistoric places
-Preserving prehistoric places for people's pleasure

OK, OK, maybe the last one's a bit silly....

So, allow me this indulgence... a bit of Shakespeare?
'Pity, you ancient stones, those tender babes' -King Richard III: IV, i 'Like stones of worth they thinly placed are, ' -Sonnets: LII