diff -Nur -Xfreecivdiff.ignore freeciv-cvs/ai/advdomestic.c freeciv-patched/ai/advdomestic.c
--- freeciv-cvs/ai/advdomestic.c	2003-07-24 17:01:32.000000000 +0100
+++ freeciv-patched/ai/advdomestic.c	2003-07-24 17:04:14.000000000 +0100
@@ -479,6 +479,11 @@
       || !can_build_improvement(pcity, id))
       continue;
 
+    if (id == B_CITY) {
+      /* if (!built_elsewhere(pcity, B_WALL)) was counterproductive -- Syela */
+      values[id] = ai_eval_threat_land(pplayer, pcity);
+    }
+
     switch (id) {
     
     /* food/growth production */
@@ -605,10 +610,6 @@
      * anyway. It was so stupid, AI wouldn't start building walls until it was 
      * in danger and it would have no chance to finish them before it was too 
      * late */
-    case B_CITY:
-      /* if (!built_elsewhere(pcity, B_WALL)) was counterproductive -- Syela */
-      values[id] = ai_eval_threat_land(pplayer, pcity);
-      break;
     case B_COASTAL:
       values[id] = ai_eval_threat_sea(pplayer, pcity);
       break;
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/client/packhand.c freeciv-patched/client/packhand.c
--- freeciv-cvs/client/packhand.c	2003-07-24 17:02:26.000000000 +0100
+++ freeciv-patched/client/packhand.c	2003-07-24 17:04:14.000000000 +0100
@@ -1211,6 +1211,22 @@
   game.nuclearwinter=pinfo->nuclearwinter;
   game.cooling=pinfo->cooling;
   if (!can_client_change_view()) {
+    /* Nasty kludge to let old code which assumes B_PALACE and B_CITY work */
+    B_PALACE = get_improvement_for_effect(NULL, EFT_CAPITAL_CITY, UCL_LAST);
+    if (B_PALACE == B_LAST) {
+      freelog(LOG_ERROR, "Cannot find any capital city improvement");
+      exit(EXIT_FAILURE);
+    }
+
+    B_CITY = get_improvement_for_effect(NULL, EFT_UNIT_DEFEND, UCL_LAND);
+    if (B_CITY == B_LAST) {
+      B_CITY = get_improvement_for_effect(NULL, EFT_UNIT_DEFEND, UCL_LAST);
+    }
+    if (B_CITY == B_LAST) {
+      freelog(LOG_ERROR, "Cannot find any city walls improvement");
+      exit(EXIT_FAILURE);
+    }
+
     improvement_status_init(game.improvements,
 			    ARRAY_SIZE(game.improvements));
 
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/common/city.c freeciv-patched/common/city.c
--- freeciv-cvs/common/city.c	2003-07-24 17:02:53.000000000 +0100
+++ freeciv-patched/common/city.c	2003-07-24 17:04:14.000000000 +0100
@@ -219,10 +219,10 @@
 	&& city_affected_by_wonder(pcity, B_MICHELANGELO))
       return TRUE;
     break;
-  case B_CITY:  
+/*case B_CITY:  
     if (city_affected_by_wonder(pcity, B_WALL))
       return TRUE;
-    break;
+    break;*/
   case B_HYDRO:
   case B_POWER:
   case B_NUCLEAR:
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/common/improvement.c freeciv-patched/common/improvement.c
--- freeciv-cvs/common/improvement.c	2003-07-24 17:02:26.000000000 +0100
+++ freeciv-patched/common/improvement.c	2003-07-24 17:04:14.000000000 +0100
@@ -28,6 +28,8 @@
 
 #include "improvement.h"
 
+int B_CITY, B_PALACE;
+
 /* get 'struct ceff_vector' functions: */
 #define SPECVEC_TAG ceff
 #define SPECVEC_TYPE struct eff_city
@@ -1263,3 +1265,28 @@
               || imeff->aff_terr == T_UNKNOWN || imeff->aff_terr == aff_terr)
              || imeff->aff_spec & aff_spec);
 }
+
+/**************************************************************************
+  Returns the index of the improvement which provides the given effect
+  (constrained to the given unit class and player, if not UCL_LAST and
+  NULL respectively) or B_LAST if no suitable improvement could be found.
+**************************************************************************/
+Impr_Type_id get_improvement_for_effect(struct player *pplayer,
+                                        enum effect_type id,
+                                        Unit_Class_id aff_unit)
+{
+  int impr;
+  struct impr_effect *eff;
+
+  for (impr = 0; impr < game.num_impr_types; impr++) {
+    for (eff = improvement_types[impr].effect;
+         eff && eff->type != EFT_LAST; eff++) {
+      if (eff->type == id
+          && (!pplayer || can_player_build_improvement(pplayer, impr))
+          && is_unit_terrain_affected(eff, aff_unit, T_UNKNOWN, S_ALL)) {
+        return impr;
+      }
+    }
+  }
+  return B_LAST;
+}
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/common/improvement.h freeciv-patched/common/improvement.h
--- freeciv-cvs/common/improvement.h	2003-07-24 17:02:53.000000000 +0100
+++ freeciv-patched/common/improvement.h	2003-07-24 17:04:14.000000000 +0100
@@ -45,9 +45,9 @@
 #ifdef OLD_IMPR_TYPE_ENUM
 enum improvement_type_id {
   B_AIRPORT=0, B_AQUEDUCT, B_BANK, B_BARRACKS, B_BARRACKS2, B_BARRACKS3, 
-  B_CATHEDRAL, B_CITY, B_COASTAL, B_COLOSSEUM, B_COURTHOUSE,  B_FACTORY, 
+  B_CATHEDRAL, B_orCITY, B_COASTAL, B_COLOSSEUM, B_COURTHOUSE,  B_FACTORY, 
   B_GRANARY, B_HARBOUR, B_HYDRO, B_LIBRARY, B_MARKETPLACE, B_MASS, B_MFG, 
-  B_NUCLEAR, B_OFFSHORE, B_PALACE, B_POLICE, B_PORT, B_POWER,
+  B_NUCLEAR, B_OFFSHORE, B_orPALACE, B_POLICE, B_PORT, B_POWER,
   B_RECYCLING, B_RESEARCH, B_SAM, B_SDI, B_SEWER, B_SOLAR, B_SCOMP, 
   B_SMODULE, B_SSTRUCTURAL, B_STOCK, B_SUPERHIGHWAYS, B_SUPERMARKET, B_TEMPLE,
   B_UNIVERSITY,  
@@ -61,6 +61,11 @@
 };
 #endif
 
+/* Some code checks explicitly for City Walls or Palace - as a temporary
+   fix, set these to the indices of improvements which provide the
+   EFT_UNIT_DEFEND (aff_unit=Land) and EFT_CAPITAL_CITY effects */
+extern int B_CITY, B_PALACE;
+
 /* B_LAST is a value which is guaranteed to be larger than all
  * actual Impr_Type_id values.  It is used as a flag value;
  * it can also be used for fixed allocations to ensure ability
@@ -393,6 +398,9 @@
 bool is_wonder_useful(Impr_Type_id id);
 Impr_Type_id find_improvement_by_name(const char *s);
 void improvement_status_init(Impr_Status * improvements, size_t elements);
+Impr_Type_id get_improvement_for_effect(struct player *pplayer,
+                                        enum effect_type id,
+                                        Unit_Class_id aff_unit);
 
 /* player related improvement and unit functions */
 bool could_player_eventually_build_improvement(struct player *p, 
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/common/player.c freeciv-patched/common/player.c
--- freeciv-cvs/common/player.c	2003-07-24 17:03:11.000000000 +0100
+++ freeciv-patched/common/player.c	2003-07-24 17:04:14.000000000 +0100
@@ -447,7 +447,7 @@
 struct city *find_palace(struct player *pplayer)
 {
   city_list_iterate(pplayer->cities, pcity) 
-    if (city_got_building(pcity, B_PALACE)) 
+    if (city_got_building(pcity, B_PALACE))
       return pcity;
   city_list_iterate_end;
   return NULL;
diff -Nur -Xfreecivdiff.ignore freeciv-cvs/server/ruleset.c freeciv-patched/server/ruleset.c
--- freeciv-cvs/server/ruleset.c	2003-07-24 17:03:11.000000000 +0100
+++ freeciv-patched/server/ruleset.c	2003-07-24 17:04:14.000000000 +0100
@@ -1283,6 +1283,22 @@
     b->helptext = lookup_helptext(file, sec[i]);
   }
 
+  /* Nasty kludge to let old code which assumes B_PALACE and B_CITY work */
+  B_PALACE = get_improvement_for_effect(NULL, EFT_CAPITAL_CITY, UCL_LAST);
+  if (B_PALACE == B_LAST) {
+    freelog(LOG_ERROR, "Cannot find any capital city improvement");
+    exit(EXIT_FAILURE);
+  }
+
+  B_CITY = get_improvement_for_effect(NULL, EFT_UNIT_DEFEND, UCL_LAND);
+  if (B_CITY == B_LAST) {
+    B_CITY = get_improvement_for_effect(NULL, EFT_UNIT_DEFEND, UCL_LAST);
+  }
+  if (B_CITY == B_LAST) {
+    freelog(LOG_ERROR, "Cannot find any city walls improvement");
+    exit(EXIT_FAILURE);
+  }
+
   /* Some more consistency checking: */
   impr_type_iterate(i) {
     b = &improvement_types[i];