I am an undergrad interested in history.

Usually when I am reading history books I find having a map along side the reading helps me alot in understanding the context and ramification of the historical events happened.

I have found a couple of sites that provide historical maps, but most are ballparks and not very detailed. This make it hard to study periods for which territory ownership change frequently.

Furthermore sometimes I don't even know if the site is trustworthy or not. And doing my own validation really defeat the purpose of using the site in the first place.

Can someone recommend some online historical map resources?

Side question: is Thomas Lesserman's website a good resource?