Notre Dame de Paris (begun 1160 AD)
In the late 1100s and early 1200s AD, the kings of France, whose capital was Paris in the north, managed to conquer the south of France and make it part of their kingdom. Now all the tax money that had been used to build Christian churches and castles in the south of France came to Paris instead, and finally the people of northern France could afford to build big stone buildings. They didn't waste any time!
In the south, people had been building churches in the Romanesque style, but for these new churches, the architects wanted a new style, which we call Gothic. The easiest difference to see between the two styles is that while Romanesque churches have round arches, Gothic churches have pointed arches.
But there are a lot of other differences as well. Gothic cathedrals have many more windows, and much bigger windows, and so they are not dark like Romanesque churches. In the hot south, people liked thick walls and small windows, so the churches would be shady and cool. In the north, where the days were darker and shorter, people wanted more light. So the architects figured out new ways of making roofs and of supporting walls, especially the groin vault and the flying buttress.
Gothic churches are also usually bigger than Romanesque churches. By 1200 AD, people had more money available, and they could afford to spend more on building great churches. And, where many Romanesque churches had wooden roofs (which were always catching fire), Gothic churches had safer stone roofs.
Check out some Gothic cathedrals (click on the picture):
St. Denis, France
(begun 1130s AD)
Rouen cathedral, France
(begun 1202 AD)
Reims cathedral, France
(begun 1211 AD)
Milan cathedral, Italy
(begun 1336 AD)
Learn by doing: visit a big church near your house.
The church at Laon