Updated at 11:47 a.m.
Note: We originally posted this item in April. With presidents Obama and Bush set to meet once again at a wreath-laying ceremony in Tanzania on Tuesday, it's worth another look back at some of the most memorable occasions during which presidents have crossed paths with one another.
Below are some moments from historian Michael Beschloss, along with a handful of others we have added.
1. A presidential quorum:
All five living presidents gathered in Dallas earlier this year for the dedication of George W. Bush's presidential library.
2. 43 and 44 together at the White House:
George W. Bush returned to the White House in 2012 for the unveiling of his official portrait.
3. Coming together for Haiti:
Bush and Bill Clinton put party differences aside in 2010 to respond to the deadly earthquake in Haiti.
4. Looking to the sky at George H.W. Bush's library dedication:
Then-president Clinton and his predecessor were spotted looking to the sky in 1997 at the dedication of George H.W. Bush's presidential library, making for a unique photo-op.
5. Nixon's funeral:
In 1994, Clinton, George H.W. Bush, Ronald Reagan, Jimmy Carter and Gerald Ford attended the funeral of the 37th president.
6. The day Clinton and George H.W. Bush drank sodas with George Wallace:
As vice president in 1982, Bush hosted governors at his Maine house, including these from Arkansas and Alabama.
7. Nixon Agonistes:
A tense White House moment between President-elect Nixon and Lyndon B. Johnson. LBJ was still furious at Nixon's secret pre-election machinations to undermine his Vietnam peace talks, and Nixon was afraid LBJ would reveal them to the world.
8. You do not do that in my Texas!
During the 1960 campaign at the Amarillo airport, vice-presidential candidate Johnson was furious when Republican pilots tried to drown out his Democratic running mate.
AUDIO BONUS: Last call
On Jan. 2, 1973, Nixon talked with former president Johnson for the last time — and recorded it on the system made famous by the Watergate scandal. The topic: attending the funeral of former president Harry S. Truman.
RELATED: The men of steel are melting with age: The Post's David von Drehle's glorious on-deadline essay on the meeting of former presidents and others at the April 1994 funeral of Richard Nixon.