Well, if my memory of Dante serves me right, those who have never heard the gospel, as well as "notable heretics", ie. people of different religions who lived righteous lives(for example Saladin), spends some time in Limbo, until they are judged by their actions and go to paradise(o not...).
I don't think it was because of not having read or heard the gospel (reading biblical texts was a privilige of the higher clergy) but because of not receiving the Holy Sacraments, including baptism.

Also if you're in limbo you stay there, you're thinking of Purgatory.