Question: What are the countries for which History of Trier principal to?
SPARQL query: SELECT DISTINCT ?uri WHERE {?uri <http://dbpedia.org/ontology/capital> <http://dbpedia.org/resource/History_of_Trier>  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Country>}
Answer: The countries with History of Trier as principal place are [Roman Empire, Gallic Empire, Praetorian prefecture of Gaul].