▁assumed ▁that ▁most ▁portal ▁tomb s ▁were ▁originally ▁covered ▁by ▁ear then ▁m ounds . ▁ ▁The ▁second - most - common ▁tomb ▁type ▁is ▁the ▁passage ▁grave . ▁It ▁normally ▁consists ▁of ▁a ▁square , ▁circular , ▁or ▁cru c iform ▁chamber ▁with ▁a ▁sl ab bed ▁or ▁cor bel led ▁roof , ▁accessed ▁by ▁a ▁long , ▁straight ▁passage way , ▁with ▁the ▁whole ▁structure ▁covered ▁by ▁a ▁circular ▁m ound ▁of ▁earth . ▁Sometimes ▁it ▁is ▁also ▁surrounded ▁by ▁an ▁external ▁stone ▁ker b . ▁Prom inent ▁examples ▁include ▁the ▁sites ▁of ▁Br ú ▁na ▁B ó in ne ▁and ▁Car row more ▁in ▁Ireland , ▁Ma es ▁How e ▁in ▁Or k ney , ▁and ▁G av rin is ▁in ▁France . ▁ ▁The ▁third ▁tomb ▁type ▁is ▁a ▁diverse ▁group ▁known ▁as ▁gallery ▁gra ves . ▁These ▁are ▁ax ial ly ▁arranged ▁ch amb ers ▁placed ▁under ▁el ong ated ▁m ounds . ▁The ▁Irish ▁court ▁tomb s , ▁British ▁long ▁bar rows , ▁and ▁German ▁Ste ink isten ▁belong ▁to ▁this ▁group . ▁ ▁Stand ing ▁stones , ▁or ▁men h irs ▁as ▁they ▁are ▁known ▁in ▁France , ▁are ▁very ▁common ▁throughout ▁Europe , ▁where ▁some ▁ 5 0 , 0 0 0 ▁examples ▁have ▁been ▁noted . ▁Some ▁of ▁these ▁are ▁thought ▁to ▁have ▁an ▁astronom ical ▁function ▁as ▁a ▁marker ▁or ▁for es ight . ▁In ▁some ▁areas , ▁long ▁and ▁complex ▁" align ments " ▁of ▁such ▁stones ▁exist , ▁the ▁largest ▁known