Created by the Greeks, the Catapult has been used since ancient times. Being able to launch fatal projectiles from a distance over structures and without explosives, the Catapult has been proven one of the most effiecient mechanisms of warfare (in history).
Used in countless wars (being re-named different things), the Catapult shot everything from rocks, greek fire, and even hand grenades (the French in WWI).
Soon when Technology progressed, the Mortar replaced the Catapult (other than Pumpkin Chunckin').
The Mortar, possibly created by Fatih Sultan Mehmed around 1450, was more efficient at launching deadly projectiles in the air than the Catapult. The first introduced Mortars were too heavy to be easily transported and fired cannonballs, making them a good weapon for defense. Soon the Mortar was transformed into a improvised Mortar, where it could be easily transported and fired new Mortar shells.
Mortars are still used to this day by many countries.
Remember as these buildings need no access. You can encapsulate them within a Wall for extra defense with no Gate, unless you want to connect more buildings to the City Center via the Road for more City Center Hitpoints.