We have a long strip of paper on the wall that is a timeline. Mostly, the girls and I have added things directly relevant to them, such as their births, when Pete and I got married, etc. We've also added historical dates that the girls are familiar with, including the sinking of the Titanic, the dates of WWII, when the Statue of Liberty and the Sears Tower were built (we've visited both places) -- in short, things that are more recent. Graceful came to me this weekend, with a furrow in her brow and said, "Mommy, William the Conqueror is missing. We need to add him."
But of course, because every 8 year old knows about William the Conqueror.