When the Berlin Wall came down a decade ago it seemed that a symbol of hopelessness had disappeared and that its lesson would be that no one should want to build anything similar ever again.
Unfortunately the lesson has not been learnt. Ugly, repellent walls remain in many countries Northern Ireland is one and now a new one is to be built between Israel and Palestine.
This is to be a 65mile security fence, the first stage of a much longer structure that will eventually divide Israel and the Palestinian West Bank.
Israel's reason for spending $200 million on this fence is that it will keep out Palestinian terrorists, especially suicide bombers.
Whether it will effectively do must be open to doubt but what is already clear is that if will not help the efforts being made to move forward a political process towards peace.
The line chosen for the fence is highly sensitive because in parts it will intrude by up to three miles into Palestinian territory thus raising suspicions that it may represent an attempt to redraw of border agreements.
At the same time Israelis living in some of the remoter of the 150 illegal settlements may find themselves on the wrong side of the security fence and thus increasingly open to Palestinian attack.