The task falls to 600 Israeli policemen with the unique beat represented by the warren of alleys enclosed within the Ottoman walls of Sultan Suleiman the Magnificent.
In other cities, the worst that police have to fear if a public order incident gets out of hand is a riot.
In Jerusalem, the worst case scenario hardly bears thinking about. A bloody clash near the holy places could trigger a new Palestinian "intifada", or uprising.
Any perceived threat to the sanctity of the Al-Aqsa mosque and the Dome of the Rock would cause fury across the Muslim world.
The atmosphere is particularly febrile at present because of the frequent stabbing attacks by Palestinians against Israelis, with 110 incidents since last October.
The risks prey on the mind of Superintendent Micky Rosenfeld of the Israeli police.
"If you have 50 people who get trampled to death in a stampede near the Western Wall, what does that mean?" he asked. "Catastrophe. The consequences won't just be in Israel - they'll be worldwide."
Some 320 CCTV cameras monitor the Old City and there are police posts every 30 to 50m.
A 40-strong rapid reaction squad is on permanent alert beside the Western Wall.
Left unspoken is one underlying cause of tension. The Old City is contested territory. Israel captured the area in 1967, but its rule is not recognised by the international community, let alone the Palestinians.
Londoners might question the Met's competence, but not its right to be everywhere in London. Israeli police have no such luxury: in the Old City, their very presence is a matter of dispute.