A snaking metal fence that divides the Gaza Strip from Israel has become the latest focal point in a generations-long conflict between Arabs and Jews in the area.

It was along this fence that at least 60 Palestinians were killed and many hundreds wounded on Monday as thousands converged to protest what they call an arbitrarily enforced demarcation line by an occupier. As protesters rushed toward the fence, some throwing rocks or homemade fire bombs, Israeli soldiers fired live bullets, which the Israeli military said was done as a last resort.

What are the fence’s origins and purpose in separating Gaza, a 25-mile-long, five-mile-wide Mediterranean coastal enclave where nearly two million Palestinians live? Is the fence recognized as an international border? And how has Israel justified deadly force to stop mostly unarmed Palestinians from breaching it? Here are the basics:

What is the fence?

The fence is actually two parallel barriers built by the Israelis: a formidable one of barbed-wire within Gaza and a 10-foot-high metal “smart fence” packed with surveillance sensors along the Israel demarcation line. A restricted buffer zone as wide as 300 yards is between them. Israel has warned that people in the zone without authorization risk being subjected to deadly force.