Ludovico Sforza ruled the state of Milan with an iron fist.

But his position is tenuous.

He is the Regent, so will only stay in power until his nephew, the rightful heir, comes of age.

Quite a lot of these city states have kind of bully boy families that have clubbed and stabbed their way into power.

Those families were walking a precipice a lot of the time.

Sforza has built a reputation as a ruthless ruler, but he has enemies on all side.

As the northernmost Italian state, Milan faces a threat from the Kingdom of France to the northwest, and constant aggression from rival states to the south.

Leonardo knows that the Duke of Milan is always in battle.

Fighting the other Italian city states.

And so he realizes that the best way to get a job is not to say I can paint Madonnas, but instead say I can make weapons of war.

He ends up writing what may be the best job application letter in history.

It's... “Hey, I'm a really good engineer...

So if you want somebody who understands warfare, if you want somebody who can build you a cannon, I'm your man.” He only mentions the fact that, “Yeah, I could decorate all your palaces too”, at the end of the letter.

I think Sforza gets exactly what he wants.

And especially at that point when it's looking like the whole peninsula is just going to explode into war.

Leonardo joins Sforzas court in Milan and pleases his patron with everything from war machines to theatrical stage sets.

He's also given free rein to immerse himself in study and invention, and to enjoy the intellectual freedom of Renaissance ideas.

Like many other Renaissance artists, Leonardo really is starting to look at things with new eyes.

People like Leonardo are reading text which is saying, look at the world around you.

Look at the natural world.

Look at the body that we are given.

Look at the heavens around you.

Study them.

Analyse them.

Now, for an artist, this is just, this is catnip, this is brilliant.