I can't remember which ancestry site it was, but it was one of the free ones.
I got quite excited when the line I was following was already filed in by someone else, as happens on such sites, so I followed it back and got excited when it got to near 1066. I left it as I had to go out, and when I came back followed another line that went even further, and into a lot of Norse Kings etc. It then went even further back or I could check other lines for Roman Emperors etc.
Whoever had completed it, had taken the time to make the linkages historically accurate, even going through the bible for who begat who, getting right back to Adam and Eve on some links, and a less religious origin on others even further back.
The downside was that they'd taken a leap of faith and some imaginary connections to get from the modern era onto the more historic stuff. Was funny to see it though.