The Dome and the hallowed Al-Aqsa mosque lie on a plaza known to Judaism as Temple Mount, and called the Noble Sanctuary by Muslims.
The glittering Dome dominates the skyline of old Jerusalem and overlooks the Western Wall, a remnant of the Jewish Second Temple, destroyed by the Romans in AD 70. The Wall is one of the holiest sites in Judaism.
Temple Mount has been a repeated flashpoint for decades. In September 2000, Ariel Sharon visited the site accompanied by a powerful security force. He claimed he was on a mission of peace, but his foray sparked a deadly riot and touched off the second intifada, or Palestinian uprising in which thousands died.
"Planning and logistics required on a trip like this can be complicated and unfortunately we weren't able to make it work in a manner that satisfied the security organizations involved," Harper spokesman Jason MacDonald said of the decision to cancel the visit.
"Specifically, Shin Bet (Israeli security) would not guarantee that they would not enter the mosque."
As many as two dozen Palestinians were killed in 1990 in riots that broke out near the mosque.
The plaza has been the site of repeated violent demonstrations, clashes, stonings and shootings, despite being steeped in religious symbolism for Jews, Christian and Muslims alike.
In Jewish belief, the two ancient temples sat over the rock where the patriarch Abraham went to sacrifice his son Isaac before an angel stopped him.
For Muslims, the rock marks the spot from which Muhammad ascended to heaven.
For Christians, the Second Temple played a key role in the life of Jesus.
The Dome and the mosque date from the seventh century. The mosque was seriously damaged several times by ancient earthquakes, although the sturdier Dome stood up to the tremors.
During the Crusades, they were used as a church and a palace before returning to Muslim control.
For the next 700 years, non-Muslims were banned from the area, until the Israelis conquered East Jerusalem during the Six-Day War in 1967.
Since then, access has varied. Although the area is occupied by Israel, the Temple Mount is actually administered by a religious trust based in Jordan. There were times when non-Muslims were barred as the political situation grew overheated. Today, non-Muslims can tour parts of the site under strict security.
The Dome and the mosque are a focal point for extremists of many stripes. Some radical Jewish groups say the structures should be razed and a new temple erected. It's a view shared by some Christian fundamentalists who believe rebuilding the temple will hasten the Second Coming.
Some Muslims see these as serious threats to a site which is regarded as the third holiest in Islam, outside of Mecca and Medina.
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