The process whose specific outcome is the progression of the pallium over time, from its formation to the mature structure. The pallium is the roof region of the telencephalon. [ GOC:cls http://purl.obolibrary.org/obo/go/references/0000021 GOC:jid GOC:dgh http://www.ncbi.nlm.nih.gov/pubmed/12626695 GOC:dph ]