How do you move goods from here to there, if you want to do so? People have been moving things from here to there since there were people. Sometimes this was out of necessity, as they moved from camp to camp and settlement to settlement. Other times it was swapping excess for excess (I have bison meat, you have maize, let’s make a deal.) As the number of people increased, the distances covered increased. I suspect the first long-distance traders were the odd souls who just couldn’t settle down. They were always looking over the next hill, and brought back what they found. But at a certain point, if you want things from far away, and in bulk, the question becomes how do you move stuff?
Obviously, you have to carry your stuff. Now, do you do this on your back, with pack-animals, or some other means? Until the Bronze Age in Europe you used muscle power alone. Unless you were fortunate and could use water, first by canoes and then by small boats. But you needed to be in sheltered waters, like the Mediterranean, or later the Baltic (in summer). And that left all the areas not along the coast or on major rivers where you still had to carry your stuff yourself. You are not going to be able to export timer this way, or large jars of oil and wine.
This is where wheels come in handy, at least if you have grasslands or flattish terrain that is not swampy or full of forests too thick to travel through.
One of the most important ways to distinguish a Halstatt or La Tene grave from others is finding the remains of a cart or wagon. The Celts traveled everywhere, including to the next life, in carts. And they introduced them to the rest of Europe north of the Alps, or where they settled. Horse harnesses, ox harnesses, wooden wheels on an axle, sometimes with metal around them, and they could carry more stuff, including bulky items. But it was not fast. If you wanted fast, you needed to go by boat. If you couldn’t boat, you got there when you got there, so no shipping produce. To travel along the southern coast of the Baltic took weeks by foot and days by boat. But exchanges happened, a lot of exchanges.
The Norse got around. Oh did they get around. Why they got around is open to debate, but between 500-1200 you almost couldn’t go to sea, or up a major river, without tripping over a Viking (Norseman, or Norman). We tend to think of them as raiders in horned hats who sacked and looted churches, terrorized the Franks, and were sort of the teenaged gangs of Late Antiquity. Well, they were, but they also traded and founded several important states, such as Kieven Rus, and served as the bodyguards for the Byzantine Emperors. When they weren’t sacking and looting and leaving genetic traces all over Europe.
Boats. The Vikings went to the afterlife in boats. They terrorized Europe in boats. They traded in boats. They founded states and colonies using boats. And you can move a lot of goods, cheaply, and quickly, in boats. And they require less labor than does overland transport, because among other things you are not caring for your animals as well as your people and cargo. One of Russia’s problems was always trade from east to west, at least once Muscovy replaced Rus as the main center of culture and power. Russia, like other parts of Europe, has north-south rivers but not many east-west rivers. The Danube was critical because it ran east-west and was navigable above the Iron Gates and below the Iron Gates.
Until the development of trains (!), it was far, far easier, cheaper, and faster to send goods by ship than overland. All the major cultural centers and capitals are on coasts, bays, or rivers, if you look closely, because of communication and trade. Why did the Portuguese, Dutch, Spanish, and others try to find a sea route to Asia? Not just for political reasons, but because you could get the good stuff in bulk and bring it home faster and more easily. Like the Vikings did.