Since the start of the second intifada in September 2000, seven government committees and five cabinet decisions have called for the construction of a barrier separating Israel from the West Bank. But they were ignored, even as Israeli fatalities and the military's plans for the barrier piled up, until, a decade ago this week, the government decided to start building.

Today 60 percent of the planned 815-kilometer route - almost three times the length of the Green Line - has been completed. That has cost the state more than NIS 11 billion so far, and maintenance costs come to about NIS 1 billion a year. There are currently still three large gaps along the Green Line, and the majority of the big blocs - Gush Etzion, Ma'aleh Adumim and Ariel-Kedumim - are outside the barrier that has been built. If that is the case, what can be learned from one of the longest-running and most expensive projects in the history of the State of Israel?

We have learned that Israel is in need of a physical barrier between it and the Palestinian territories in any scenario, whether confrontation or negotiated agreement. This need springs from the ongoing threat of terror, of varying levels of intensity, on both sides. Of no less importance, the need springs from the financial gap between the sides that is unequalled anywhere - Israel has 15 times the gross domestic product per capita of the Palestinian territories - that motivates tens of thousands of Palestinians to seek work in Israel, whether or not they have permits to do so. This slowly leads to a Palestinian "return" to Israel.

A barrier on an agreed border line should be in the Israeli interest, since Israel would then be able to ensure that the border between it and Palestine is relatively porous, enabling the passage of goods, tourists, workers and vehicles. Building the barrier with security needs in mind will make it easier for Israel, when it signs an agreement, to prevent opponents on both sides from interfering with the implementation of a deal through violent acts, mass marches and so forth.

We have learned that the Israeli public had enough power to determine that a barrier must be built, despite the firm opposition on the part of the country's leaders at the time: Prime Minister Ariel Sharon, Defense Minister Benjamin Ben-Eliezer and IDF Chief of Staff Shaul Mofaz and his deputy Moshe Ya'alon, along with settler leaders and their representatives in the Knesset. And by means of the High Court of Justice, the public also had enough power to bring about a dramatic change in the route of the barrier, ultimately making it more secure. The barrier was originally meant to create a de facto annexation of some 20 percent of the West Bank, but this was reduced to 8 percent in the altered plans; when those plans were implemented, the proportion was reduced further, to 5 percent.

We have learned that all the Israeli governments since Sharon's have been inclined to revise the barrier's route on the basis of political considerations that take the needs of settlements into account, considerations that are alien to real security needs. They have done so even at the price of leaving gaps in the barrier that terrorists and Palestinian workers were able to penetrate - and of endangering the forces patroling the barrier, according to the High Court of Justice. The price for Israel's behavior also includes "a lack of in-depth judgment and considerations of all the security and economic factors" regarding the barrier, according to the 2007 Brodet report on the security budget. During construction of the barrier, some NIS 2 billion was wasted over the re-planning and rebuilding needed to change the route, and unnecessary harm was caused to the fabric of Palestinian life and to the environment, the landscape and historical sites.

Yet another lesson learned was that a barrier following the same route as the permanent border proposed by Ehud Barak in 2001 and Ehud Olmert in 2008 created the illusion in the eyes of the Israeli public that Israel had reached an agreement with the Palestinians on the matter. This gave rise to two contradictory, or perhaps complementary, conceptual trends. One was the idea of bringing isolated settlements within the range of the barrier and expanding settlements that were already enclosed by it. The other was the idea of massive construction on isolated settlements while dozens of unauthorized outposts would be built, with the intention of creating a "corridor" of Jewish construction between the isolated settlements and outposts and the more established settlement blocs. Thus did the underlying concept behind the construction of the barrier - "We are here and they are there" - fade into the ether.