The Silk Road and other trading routes were very in existence at the time of Polo's journey and would have provided markets, towns, and cities for him to utilize along the way.It would have been a difficult journey, especially going across two deserts, but clearly not impossible. We can look at the legs of his journey and judge for ourselves the difficulty.

1. Setting sail from Venice to Acre(It's in modern day Israel). People made this journey often, sometimes on pilgrimage and sometimes going over land through what is now Istanbul. Not a super difficult leg.

2. Acre to Hormuz. Once again, a difficult journey by our standards, but the roads were being used by many traders and there were people along the way to provide provisions.

3. Crossing the Pamir Mountains would probably have been very difficult. I can't say for sure how they survived this, but I would venture to say that it was a mix of keeping a good stock of provisions along with utilizing villages, foraging and hunting. But it's not like no one lived here, Kashgar was a stopping point on Polo's journey. He noted there were Christians living there and open air markets.

4.The journey across the Gobi was extremely difficult. It took a month and Polo notes that they took enough food to last a long time. He makes mention that food was not to be found, but that water could be found. He said it was extremely scarce, but they found enough to survive on and to reach their destination of what is now Beijing.

So to summarize, a mix of utilizing existing trade routes, villages and cities, and some foraging of water and resources.

On a related note, can anyone recommend a good book abou Marco Polo's travels? Is it worth it for a layperson to try reading his writings directly?

I've always wondered, was sailing to Tianjin/Beijing not possible during this time? I mean sailing from Hormuz for example. Were ships not good enough or was it just too slow/expensive?