Just finished reading Secrets of the Druids, a serious work and an enjoyable read.
A wealth of Celtic and proto-Celltic lore, seemingly well researched histories of people's migrations (from about 4000 BC) across the old world from India to Ireland and the Urals to Iberia;
with extensive descriptions of the customs and rites they brought with them.
The book also contains an absolute treasure of etymologies and synonyms !
Now if we could just nail the origins of the PIEs back another millennium ...
Interesting that a number of researchers have posited the geographic origins of the Sumerians to have been in the same general area as Teresa has for the (later?) PIEs.