Learning with the times: Since when have defensive walls been made to protect countries or cities?

Building walls or fortifications for defending cities or empires by restricting the entry of outsiders is as old as recorded history . Most civilizations from classical antiquity to medieval and modern times have built some sort of defensive fortification or walls for protection from outsiders.Hadrian's Wall constructed by Roman emperor Hadrian was a 73-mile wall built around 122 AD to protect Britain under Roman control from the tribes inhabiting northern England and Scotland. Existing portions of the Great Wall of China were built during the Ming Dynasty (1368-1644) to protect its area from Mongol invasion.Similar wall like fortifications were built in Greece (Athens), Iraq (Babylon), Nigeria (Benin City), Zimbabwe (Great Zimbabwe), India (hill fortresses of Rajasthan) and so on.

Which are the famous walls built in modern times?
Perhaps the most famous was the Berlin Wall. Stretching for over 100km, it was built by the communist regime ruling East Germany. Although the stated purpose of building it was to protect the citizens of East Germany from fascist elements, the wall is often seen as the state's attempt to stop the movement of East Germans to the West during the Cold War era. The wall was demolished in November 1989. Similar to the Berlin wall is the Korean Demilitarized Zone (DMZ), which acts as the de facto border between North and South Korea. The heavily militarized wall creates a 250 km long buff er zone that divides the Korean peninsula roughly in half. The Israeli West Bank barrier that was supposed to run along the 1949 Armistice Line set out in the Arab-Israel conflict is among the world's most controversial walls built to mark borders. The wall is claimed to be a security barrier by the Israeli government, but Palestinians call it a wall of racial segregation and land grab disguised as a border security wall.

Is Trump's proposed wall along the Mexican border first such attempt in the West in recent times?
The fall of the Berlin wall marked the end of the Cold War and the beginning of a more globalised world. The new world saw the formation of the European union and most of the continent became borderless. However, it seems that the apparent trend of globalisation tearing down borders was a short lived experiment as at present many European countries are also building walls to stop the influx of refugees from central Asia as well as Africa. The proposal of a wall to protect the US border from Mexican immigrants predates Trump's presidential campaign. Various barriers to check Mexican immigrants are being built since the early 1990s. Recently published news reports show that construction work for more than 20 border barriers started between 2000 and 2014, which is roughly the same as the number of barriers built in the 50 years between 1950 and 2000.