They did conquer the entirety of Gaul, which is not just coast. And France isn't small. Romans built roads, supply depots, carried supplies on pack animals. An

They did conquer the entirety of Gaul, which is not just coast. And France isn't small. Romans built roads, supply depots, carried supplies on pack animals. And if you think you can move 50,000 soldiers 500 miles deep into enemy territory without supply lines, you can forget about that too. Napoleon did use supply lines from Poland into Russia. Remember: we're talking about Sun Tzu's advice not to bring your own food but take it all from the enemy land, and I'm saying that doesn't work in all circumstances. I'm not saying it never works. But there are very good reasons why historically, large armies did rely on supply lines.