Earliest fanfic?

[rhu]

Among other things on our Manhattan day, H and I spent an hour or so at the NYPL, taking in the portrait gallery on the third floor and the "Mapping NYC" and "Candide at 350" exhibits off the lobby. Well worth it, and one thing from the Candide exhibit that struck me was the placard that described some of the early Candide-inspired derivative works as "among the earliest fan fiction."

First, how awesome is it that the concept of fanfic is mainstream enough that it can be referenced in this way?

Second, it got me wondering what earlier works could be considered fanfic. Was there contemporary fanfic on Shakespeare? Homer? Are midrashim fanfic on the Bible? "Hey, check out this Adam/Lilith slash I found!"