
Originally Posted by
Landwalker
For one, when you're traveling by land, you can live off the land, instead of having to live off supplies--you can't pillage the countryside in a boat in the middle of the Mediterranean. Similarly, consider that even a dedicated transport ship could probably transport no more than two hundred non-sailors, and that the First Crusade involved over 40,000 soldiers, not to mention the number of hangers-on, camp followers, and non-fighting pilgrims who accompanied them and pushed the total number well over 100,000. This would certainly involve far more ships than anyone could muster at one time, and probably more pure transport ships than even existed at the time.
Finally, there would have been no port for the ships to land in the East (until after the First Crusade, at least) except for Constantinople--and then they would have had to march across all of Anatolia and Syria anyway.
I'm sure there were other reasons, but these are a few of the most likely culprits that pop into my mind. Remember, however, that after the First Crusade, a lot of "crusaders" (not necessarily those involved in the "official" crusades, but the ones who trickled in) did take ships, since it was more feasible both in terms of supplies and quantity.
Cheers.