When they were built in towns they were by far the largest structures around. When most homes and businesses around were two and three floors high, and made out of wood. The Cathedrals were 8 to 12 floors high at their highest peaks, and made from stone, and had huge stained glass windows. They were easy to spot to say the least.
The Salisbury Cathedral in England, here you can clearly see how it was the largest and most seen structure in all the surrounding area.
Most if not all of these cathedrals had large glass windows high up which allowed "god's light" to shine in. This was not only symbolic, but also aesthetics to these spaces.
Light and god, have been together since the creation of men. When the sun shines through these alter spaces in these huge stone structures it would light the space immensely. It was easy for one to feel safe in the eye of the creator in this massive "temple" built in his honor, a much needed place in such hard time as the "dark ages" of Europe.
In such dark times, it was important for people of faith to have a safe haven to worship god, and these massive stone cathedrals allowed for that to happen. Few made it through the test of time, but the ones still standing, one can easily see how. With such detailed work, and such a strong building, it does seem as if god's very hand built the structure. They were the largest places in towns, and served as the cities heart and connection to the higher power. They were symbols of hope, and of salvation. These cathedrals power was everything over the towns that they were in.