2000 + Old Roman ? Mortar Antiquity Museum Quality

I've had this mortar for many years.  All I've been able to find out is it's over 2000 yrs old - I believe it is Roman and it is museum quality.  I've had it looked at by Butterfield in San Francisco, the Museum of Art & Natural History in SF, a couple local appraisers and sent photos to Sotheby but no one is able to date it more specifically than over 2000 yrs old because they are not familiar with that era and I haven't even been able to get a guesstimate on value.  I bought it many years ago at an antique street fair from a mountain man dressed in all skins he had made himself - very hairy - and it wasn't a show to attract attention and sales . he only came that one time to the show and had many very old, unique items.

II'd love to find out more about it and in particular it's value or if anyone could point me in another direction, I'd appreciate it.  Thank you'