So I'm going to travel just outside the medieval period because I was recently reading a short article about the development of Stockholm in the early 1600s which basically changes a medieval town of around 9000 into the bustling metropolis of a European Great Power in less than a century.

The capital of the Swedish empire in 1634 had around 9000 people jam packed into the central island of the Mälaren passage which makes Stockholm such a convenient spot to put a city in the medieval period along with some village-like settlement on the north and south mainland areas across from the city. This area is the modern Stockholm "Old Town" district. The buildings were mostly low wooden ones with turf roofs where goats could be found grazing. Streets were narrow and winding. While you had the royal castle, churches and of course some medieaval stonework buildings, all in all it was a rather unimpressive city for the up and coming continental power. When the "Lion of the North", Gustav II Adolf was to be buried in 1634 it was downright embarrassing for the Swedish state that the dignitaries could see how provincial their capital was and the sorry state of the capital was considered a matter of state security and foreign policy. Who'd take them seriously when they were clearly not a force to be reckoned with? So the powers at be decided to fix it. New square and rectangular road grids were laid out and houses were demolished to make way for new straight roads. Especially on the less densely built mainland bits. The rich and powerful were encouraged to build baroque palaces in the capital and Swedish successes (and plenty of looted artwork) allowed them to do so. Having also become an official capital a number of state functions became concentrated here and administration grew as more and more governance was extended into the the nation itself (much of the modern administrative features and delineations come form this period) and over new territories. This would completely change the character of the capital, from the around 9.000 inhabitants in the early 1600s there was about 35.000 in 1650 and 60.000 in 1685. Changing fortunes of war, pestilence and all the goodies the 4 horsemen bring reduced the growth considerably in the 1700s.

Now this is not exactly starting with a fishing village. At the time Stockholm was the largest and most important city in the realm, 5 times larger than the next largest town. But it shows IMO the kind of growth possible if an late-medieval/early-modern state puts it effort into it. And from a broader European perspective, at the time, Stockholm was an absolutely tiny town and decidedly backwards. And while it's a bit late for medieaval, other than the artistic styles and penchant for straight roads the actual methods of construction weren't much more advance over the medieval period anyway. As the article described it, Stockholm was fundamentally a giant construction site for decades.