Today is Jerusalem Day in Israel, the anniversary of the day in the 1967 war when Israel took the Old City and East Jerusalem from Jordan. More than 40 years later, Jerusalem remains one of the largest hurdles to resolving the Israeli-Palestinian conflict. Israel insists Jerusalem is its ‘undivided and eternal’ capital while Palestinians insist on securing a capital in East Jerusalem. Here are three reasons why Jerusalem is so important to both sides.

One capital city wanted by two nations
Jerusalem already functions as Israel’s capital. The majority of the country’s government buildings are located in West Jerusalem, the part of the city that remained under Israeli control between its independence and the 1967 war. But in Judaism, Jerusalem is considered the “eternal and undivided capital” of the Jewish nation, and many Israeli politicians – from Prime Minister Benjamin Netanyahu to Jerusalem Mayor Nir Barkat – have insisted on a unified national capital that includes East Jerusalem.

Palestinians, however, claim East Jerusalem as the capital of a future Palestinian state. The area was a part of Jordan between 1948 and 1967 and is predominantly Arab. Palestinians were so expectant that their capital would be established there they they began building a parliament building in the East Jerusalem suburb of Abu Dis in 1997, although it was abandoned when the second intifada broke out three years later. The unfinished project is now separated from Jerusalem by Israel’s concrete security barrier, as are the people it was supposed to represent.

Religious significance
The biblical King David conquered Jerusalem about 3,000 years ago, and his son Solomon built the temple on the site where Jews believe Abraham planned to offer Isaac as a sacrifice – proving his dedication to God. The site become the symbolic center of the Jewish nation.

In the 7th century AD, Muslims – who believed that the prophet Muhammad ascended into heaven from the Temple Mount area and also revere Abraham – captured Jerusalem from the Christians. Today it is among the holiest cities to Muslims after Mecca and Medina.

These Muslim and Jewish holy sites are literally on top of each other, with the Dome of the Rock and Al Aqsa mosque resting on the area where the Second Temple once stood and bordered today by the Western Wall. But while the Temple Mount is potentially the most contested, outside the Old City there are numerous sacred sites in an area known as the Holy Basin – including the Mt. of Olives cemetery, estimated to hold as many as 300,000 graves.

A final peace deal would need to resolve who will control access to these holy sites. Jews were denied access to the Old City during Jordan’s 1949-67 occupation. Muslims are technically allowed to visit the Temple Mount today, but due to numerous bureaucratic hurdles such as security permits for Palestinians and temporary restrictions such as a ban on men younger than 40, in practice many cannot visit the Temple Mount.

Sovereignty and security
Up until 1967, West Jerusalem was bordered by hostile Jordanian territory on three of its four sides. In the Six-Day War, Arab armies from Jordan, Syria, and Egypt advanced on the Jewish state, though Israel defeated them in less than a week. In the wake of the war, Israel expanded the borders of East Jerusalem to include areas deemed critical to national security, roughly tripling its size.

When Prime Minister Benjamin Netanyahu insisted last month that Israel retain “defensible borders” he presumably was alluding in part to East Jerusalem’s expanded borders, which serve as a buffer to key population centers.

However, Palestinians – backed up by the United Nations – argue that Israel’s presence in East Jerusalem constitutes an illegal occupation under international law. The expansion of Israeli building in greater East Jerusalem, they argue, undermines the viability and sovereignty of a future Palestinian state.

Palestinian sovereignty and Israeli security are not necessarily mutually exclusive, however; Israeli historian Martin van Crevels argues that from 1948 to 1967, those borders around Jerusalem were defensible. When Jordan launched its attack during the Six-Day War in 1967, Israel was able to repel Jordanian forces from territory it already held (West Jerusalem) and claim new territory (East Jerusalem and the Old City).