Two weeks ago, the famed Crusader castle Crac des Chevaliers, one of the irreplaceable Syrian heritage sites named to the 2014 World Monuments Watch, again found itself a target in the Syrian civil war.

This winter, the film "Monuments Men" told the story of how, over two years, with virtually no resources or support, a ragtag division of 345 volunteers from 17 countries working under the aegis of the Monuments, Fine Arts and Archives (MFAA) program rescued six million stolen artworks from Nazi depots, including some of the world's most esteemed masterpieces, and saved hundreds of historic buildings, objects and archival collections from destruction in Europe and Asia.

Yet there has been no sequel to the work of the Monuments Men. Time and again, major cultural treasures have been destroyed, museums looted and archaeological sites despoiled during conflicts. Even after civil law was re-established in Afghanistan, Egypt and Iraq, the destruction has continued under the noses of authorities. In Syria, cellphones have captured the obliteration of the historic center of Aleppo. The director general of antiquities in Syria reports that 420 monumental sites have been damaged in the two years since the civil war began, many in the cities of Aleppo and Homs. The costs of reconstruction would run to the hundreds of millions of dollars and require highly specialized technical capabilities. Also troubling is the widespread looting that has occurred in Afghanistan, Egypt, Iraq, Syria and Yemen during the past decade. Estimates of antiquities looting and theft in Egypt and Syria since 2011 run into the billions of dollars; but sadly, we'll never know its full extent.

Cultural heritage links us to our history and identity through structures, objects and traditions. It gives places meaning through references to the past. It enriches our quality of life, contributes to a community's economic well-being and is fundamental to a healthy society. People in places under siege are no less concerned about their heritage than those who watch from the outside. But people caught in these circumstances are often powerless to intervene, which is why we need a dedicated effort on their behalf.

Protecting cultural heritage during and in the aftermath of conflict is one of the biggest challenges facing the cultural field. Government agencies in affected countries are doing as much as possible to repair damage and recover looted property despite the limited resources available. But rather than waiting for the damage to occur, we need to do more to prepare for such situations and reduce the likelihood of catastrophic damage. There are small but important steps that would have a powerful psychological impact in times of conflict and make a significant difference afterward, as the ravished societies rebuild.

The Hague Convention for the Protection of Cultural Property in the Event of Armed Conflict, signed by the United Nations in 1954, provides the essential framework for these measures. It calls for the inventory of sites considered to be of national and international significance, which, when conflict is imminent, should bear a visible blue shield. Unfortunately, there were no blue shields in Afghanistan, Egypt, Iraq or Syria during the recent upheavals in these countries. Had there been, we might not now be mourning the loss of the Ayubbid Mosque in Syria or the destruction of artifacts at the Museum of Islamic Art in Cairo a few weeks ago.

Of course, such shields can be a mixed blessing. They have been known to attract unfriendly fire, as they did in the Balkan conflict. Still, they attest to the importance of places whose loss would impoverish all humanity. And they put warring parties on notice that they are responsible should anything befall them. A concerted effort is needed to install blue shields on monuments and sites world-wide when hostilities are imminent.

Unfortunately, the Hague cultural-property convention is universally regarded as one of the least effective of the U.N. charters. Although 126 countries have now signed it, including the U.S., there are few examples where it has been invoked by countries in areas of conflict. The treaty calls for parties "to take, within the framework of their ordinary criminal jurisdiction, all necessary steps to prosecute and impose penal or disciplinary sanctions" on those who violate the treaty, but there are almost no examples of enforcement. Countries in the developed world that are party to the 1954 Hague Convention need to begin making plans now to provide assistance in the Middle East and North Africa, where conflict is taking a daily toll on some of humanity's most precious museums and monuments. In addition, enforcement needs to be strengthened to ensure that those who do destroy cultural heritage pay a real price.

It would also help to train more people in positions of local responsibility to prepare for conflict and conduct postconflict recovery work. Today, U.N. institutions are making courses available through the Internet to heritage professionals in Syria. These efforts could be enhanced. Specialists in Egypt and Syria are doing their best to identify damage as it occurs, establish priorities and strengthen protection for heritage sites, even while conflict continues, but they have few resources.

There is hope, however. Earlier this month, the State Department invited qualified U.S. organizations to apply for support to organize a research project aimed at documenting the current condition and future preservation needs of cultural-heritage sites in Syria, as well as plans and recommendations for preservation efforts to be undertaken when conditions permit. This small program will lay the groundwork for heritage conservation when conditions improve.

The past few years have seen several gestures that, taken together, attest to a renewed interest in this important issue. In 2007, a U.S. Army resolution recognized the World War II work of the Monuments, Fine Arts and Archives program. In 2009, the U.S. adopted the Hague cultural-property convention. In December 2013, Sen. Roy Blunt of Missouri introduced a resolution to award the Congressional Gold Medal collectively to the members of the MFAA (five are still alive). The legislation is pending.

Protecting cultural heritage is not a luxury. Bring back the Monuments Men, whose unstinting service made it clear that the greatest works of civilization are worth preserving.

Ms. Burnham is president of the World Monuments Fund.