By James Robbins
BBC diplomatic correspondent
Borders - especially closed borders - divide families.
People have been ferrying goods and livestock back into Gaza
So we should not be surprised by reports that one Egyptian family responded to dramatic pictures of tens of thousands of Palestinians streaming into Egypt through the breached Rafah barriers by bringing forward the date of a wedding in the hope that cousins, normally shut off inside the Gaza Strip, might be able to join them.
Egypt is under enormous pressure - from Israel and much of the international community - to get a grip and reseal the border.
Israel fears wholesale arms smuggling to extremists in Gaza.
Other governments fear the breakdown of delicately balanced international agreements meant to reassure Israel and help open the way to a comprehensive peace - the Israel-Palestine "two-state solution".
End of arrangement
But the breaches of the past few days have drawn global attention to the near total isolation of the civilians of Gaza, so that simply closing the frontier again may prove politically all but impossible.
The border was not meant to be completely closed, of course.
At the time of Israel's "disengagement" or withdrawal from Gaza in 2005, an international agreement launched new policing of the Rafah border.
17 January: Israel seals border following rise in rocket attacks
20 January: Gaza's only power plant shuts down
22 January: Israel eases restrictions
22 January: Egyptian border guards disperse Palestinian protest against closure
23 January: Border wall breached
Essentially, a combination of CCTV cameras providing live pictures to the Israeli authorities and a team of EU monitors at crossing points was intended to ensure proper control, and protection against the smuggling of guns and explosives which could be used to launch attacks against Israel from Gaza.
Those arrangements broke down progressively, partly after Hamas won the parliamentary elections in Gaza of January 2006, and totally after the final seizure of all power in Gaza by Hamas in 2007.
The EU teams withdrew. The border closed.
It has become part of Israel's blockade of Gaza, which Israel says is a necessary response to rocket attacks from Gaza which kill and injure Israeli citizens.
Others insist the blockade amounts to illegal collective punishment of Gaza's civilian population.
Egyptian riot police have been attempting to seal the breach
Egypt is in a bind. It did not want the border breached.
The Egyptian government despises and fears Hamas. It fears opposition forces within Egypt, including religious fundamentalists, being strengthened by Hamas ideology.
But equally, Egypt does not want to be seen directly as "Gaza's jailer". So closing the border, amid scenes of Arab fighting Arab - Palestinian stones against Egyptian riot shields - is also very unwelcome.
Israel has moved to suggest that any failure to close the border by Egypt would justify Israel in handing over responsibility for the future welfare of the people of Gaza to Egypt - neatly ridding Israel of a problem, and the source of so much international criticism.
That will not happen, but the Rafah border breach and the extraordinary scenes of a mass Palestinian breakout for shopping or simply for fresh air may yet have profound political effects on the entire Middle East peace process.
The downside could be a hardening of attitudes on all sides, further complicating or poisoning the climate for concessions in the dialogue which US President George W Bush is hoping to accelerate.
The upside could be a realisation that the present situation in Gaza, and the split between Hamas there, and Fatah in the West Bank, is utterly unsustainable.
Only a comprehensive final settlement between Israelis and Palestinians offers the prospect of security, and possibly prosperity too, for all.