We stumbled upon parts of an old Roman temple
According to the signs next to the pillars, it was the center of the forum in Barcelona. The religious ceremonies would have taken place outside of the temple.
The temple was built during the 1st century BC and was in use until the 5th century AD, when the importance of the forum began to decline, due to Christianity becoming the main religion. It was no longer the center of politics, religion etc..
A Roman house mosaic
Also I just forgot the word for barbed wire and had to google "Sharp things on top of a fence"