Short answers, pulled from the story.
The settlement of Solnitsata in Bulgaria was built around 4700 BC. It stands as one of the earliest known fortified communities in human history with walls constructed from stone blocks that stood 1.5 meters high and 1.2 meters thick.
The Mycenaeans built their cyclopean walls without mortar by relying on the precise fitting of huge stones to create a defensive barrier that has stood for millennia. These walls were designed to withstand prolonged sieges and direct assaults while featuring gates that were heavily fortified to control access.
The Aurelian Walls of Rome were built to protect the city from barbarian invasions and feature massive stone blocks and strategically placed gates that controlled movement in and out of the city. These walls still stand today as a testament to Roman engineering principles applied to fortification.
The arrival of cannons in the 14th century fundamentally changed the nature of fortification by rendering medieval-style walls obsolete and forcing a complete rethinking of defensive architecture. Fortifications evolved into lower structures with greater use of ditches and earth ramparts designed to absorb and disperse the energy of cannon fire.
The Maginot Line failed to stop the German invasion because it was ultimately bypassed, demonstrating the limitations of static defensive lines in the face of mobile warfare. The rise of intercontinental ballistic missiles and the development of mobile defenses further reduced the importance of permanent fortifications.