The best way to find out about the past is to ask someone who was there. My mother remembers the Second World War. My Great Aunt, who's dead now, met the German Kaiser in Berlin just before the First World War started.

But of course, as you go back you reach a time no one alive can still remember. Then you have to read old books to find out what happened, look at pictures to see how people dressed, or visit old buildings to see how they lived.

Archaeologists can help as well. They dig underground, finding coins, rings and other things. Often, if you go a long way back in time, everything we know has to be discovered by digging underground. And often we find things we don't understand at all, and all we can do is guess.

People don't always agree about the past, just as they disagree about things happening now. Sometimes stories we've believed for years turn out to be wrong. Often historians quarrel about why things happened the way they did. To try and understand the past better, they spend hours in archives, where old letters and accounts are stored.

Working in archives doesn't sound much fun, but it can be very exciting. I wrote a book once about a time when the Duke of Monmouth tried to make himself King, but was beaten and executed. I found his pocket book in an archive. It was very old and stained, but you could still read the notes he'd made, including a recipe for invisible ink. And holding it, I could suddenly picture the Duke after losing his last battle, hiding in a hedge with the book in his pocket, while he waited for the soldiers to arrest him.