diff ai/advdomestic.c ai/advdomestic.c
--- ai/advdomestic.c	Thu Jan 11 11:01:45 2001
+++ ai/advdomestic.c	Fri Jan 12 10:35:43 2001
@@ -31,12 +31,6 @@
 
 #include "advdomestic.h"
 
-/********************************************************************** 
-... this function should assign a value to choice and want and type, where 
-    want is a value between 1 and 100.
-    if want is 0 this advisor doesn't want anything
-    type = 1 means unit, type = 0 means building
-***********************************************************************/
 
 static int ai_best_tile_value(struct city *pcity)
 {
@@ -523,7 +517,13 @@
   }
 
   return;
-}  
+}
+
+/********************************************************************** 
+... this function should assign a value to choice and want and type, where 
+    want is a value between 1 and 100.
+    if want is 0 this advisor doesn't want anything
+***********************************************************************/
 
 void domestic_advisor_choose_build(struct player *pplayer, struct city *pcity,
 				   struct ai_choice *choice)
@@ -538,7 +538,7 @@
 
   choice->choice = 0;
   choice->want   = 0;
-  choice->type   = 0;
+  choice->type   = CT_NONE;
   con = map_get_continent(pcity->x, pcity->y);
 
   utid = best_role_unit(pcity, F_SETTLERS);
@@ -553,11 +553,11 @@
       freelog(LOG_DEBUG, "%s (%d, %d) desires settlers with passion %d",
 	      pcity->name, pcity->x, pcity->y, want);
       choice->want = want;
-      choice->type = 1;
+      choice->type = CT_NONMIL;
       ai_choose_role_unit(pplayer, pcity, choice, F_SETTLERS, want);
     } else if (want < 0) { /* need boats to colonize! */
       choice->want = 0 - want;
-      choice->type = 1;
+      choice->type = CT_NONMIL;
       choice->choice = best_role_unit(pcity, F_SETTLERS); /* default */
       ai_choose_ferryboat(pplayer, pcity, choice);
     }
@@ -576,11 +576,11 @@
 	freelog(LOG_DEBUG, "%s (%d, %d) desires founders with passion %d",
 		pcity->name, pcity->x, pcity->y, want);
 	choice->want = want;
-	choice->type = 1;
+	choice->type = CT_NONMIL;
 	ai_choose_role_unit(pplayer, pcity, choice, F_CITIES, want);
       } else if (want < -choice->want) { /* need boats to colonize! */
 	choice->want = 0 - want;
-	choice->type = 1;
+	choice->type = CT_NONMIL;
 	choice->choice = best_role_unit(pcity, F_CITIES); /* default */
 	ai_choose_ferryboat(pplayer, pcity, choice);
       }
@@ -617,7 +617,7 @@
       if (can_build_unit_direct(pcity, iunit)) {
         if (want > choice->want) {
           choice->want = want;
-          choice->type = 1;
+          choice->type = CT_NONMIL;
 	  ai_choose_role_unit(pplayer, pcity, choice, F_CARAVAN, dw/2);
         }
       } else
@@ -631,7 +631,7 @@
     choice->want = cur.want;
 /*    if (choice->want > 100) choice->want = 100; */
 /* want > 100 means BUY RIGHT NOW */
-    choice->type = 0;
+    choice->type = CT_BUILDING;
   }
 /* allowing buy of peaceful units after much testing -- Syela */
 
@@ -643,7 +643,7 @@
     }
     if (iunit != U_LAST) {
       choice->want = 1;
-      choice->type = 1;
+      choice->type = CT_NONMIL;
       choice->choice = iunit;
     }
   }
diff ai/advmilitary.c ai/advmilitary.c
--- ai/advmilitary.c	Thu Jan 11 11:01:45 2001
+++ ai/advmilitary.c	Fri Jan 12 10:13:00 2001
@@ -527,7 +527,7 @@
   }
   choice->choice = bestid;
   choice->want = danger;
-  choice->type = 3;
+  choice->type = CT_DEFENDER;
   return;
 }
 
@@ -861,11 +861,11 @@
           choice->choice = B_BARRACKS2;
         else choice->choice = B_BARRACKS;
         choice->want = e;
-        choice->type = 0;
+        choice->type = CT_BUILDING;
       } else {
         if (!myunit->id) {
           choice->choice = v;
-          choice->type = 2; /* type == 2 identifies attackers */
+          choice->type = CT_ATTACKER;
           choice->want = e;
           if (needferry) ai_choose_ferryboat(pplayer, pcity, choice);
 	  freelog(LOG_DEBUG, "%s has chosen attacker, %s",
@@ -874,7 +874,7 @@
           choice->choice = ai_choose_defender(pcity);
 	  freelog(LOG_DEBUG, "%s has chosen defender, %s",
 			pcity->name, unit_types[choice->choice].name);
-          choice->type = 1;
+          choice->type = CT_NONMIL;
           choice->want = e;
         }
         if (is_sailing_unit(myunit) && improvement_exists(B_PORT)
@@ -883,7 +883,7 @@
           if (get_invention(pplayer, tech) == TECH_KNOWN) {
             choice->choice = B_PORT;
             choice->want = e;
-            choice->type = 0;
+            choice->type = CT_BUILDING;
           } else pplayer->ai.tech_want[tech] += e;
         }
       }
@@ -921,7 +921,6 @@
 ... this function should assign a value to choice and want and type, 
     where want is a value between 1 and 100.
     if want is 0 this advisor doesn't want anything
-    type = 1 means unit, type = 0 means building
 ***********************************************************************/
 void military_advisor_choose_build(struct player *pplayer, struct city *pcity,
 				    struct ai_choice *choice)
@@ -935,7 +934,7 @@
   struct unit *aunit = 0;
   choice->choice = 0;
   choice->want   = 0;
-  choice->type   = 0;
+  choice->type   = CT_NONE;
 
 /* TODO: recognize units that can DEFEND_HOME but are in the field. -- Syela */
 
@@ -954,7 +953,7 @@
        freelog(LOG_DEBUG, "A diplomat will be built in city %s.", pcity->name);
        choice->want = 16000; /* diplomat more important than soldiers */ 
        pcity->ai.urgency = 1;
-       choice->type = 3; /* defender */
+       choice->type = CT_DEFENDER;
        choice->choice = u;
        return;
     } else if (num_role_units(F_DIPLOMAT)>0) {
@@ -987,7 +986,7 @@
       choice->choice = B_CITY; /* great wall is under domestic */
       choice->want = pcity->ai.building_want[B_CITY]; /* hacked by assess_danger */
       if (!urgency && choice->want > 100) choice->want = 100;
-      choice->type = 0;
+      choice->type = CT_BUILDING;
     } else if (pcity->ai.building_want[B_COASTAL] && def &&
         can_build_improvement(pcity, B_COASTAL) &&
         (danger < 101 || unit_list_size(&ptile->units) > 1) &&
@@ -995,7 +994,7 @@
       choice->choice = B_COASTAL; /* great wall is under domestic */
       choice->want = pcity->ai.building_want[B_COASTAL]; /* hacked by assess_danger */
       if (!urgency && choice->want > 100) choice->want = 100;
-      choice->type = 0;
+      choice->type = CT_BUILDING;
     } else if (pcity->ai.building_want[B_SAM] && def &&
         can_build_improvement(pcity, B_SAM) &&
         (danger < 101 || unit_list_size(&ptile->units) > 1) &&
@@ -1003,7 +1002,7 @@
       choice->choice = B_SAM; /* great wall is under domestic */
       choice->want = pcity->ai.building_want[B_SAM]; /* hacked by assess_danger */
       if (!urgency && choice->want > 100) choice->want = 100;
-      choice->type = 0;
+      choice->type = CT_BUILDING;
     } else if (danger > 0 && unit_list_size(&ptile->units) <= urgency) {
       process_defender_want(pplayer, pcity, danger, choice);
       if (!urgency && unit_types[choice->choice].defense_strength == 1) {
@@ -1037,7 +1036,7 @@
     if (want > choice->want) {
       choice->want = want;
       choice->choice = v;
-      choice->type = 1;
+      choice->type = CT_NONMIL; /* Why not CT_DEFENDER? -- Caz */
     }
   }
 
diff ai/aicity.c ai/aicity.c
--- ai/aicity.c	Thu Jan 11 11:01:45 2001
+++ ai/aicity.c	Fri Jan 12 06:41:02 2001
@@ -14,6 +14,7 @@
 #include <config.h>
 #endif
 
+#include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -184,7 +185,7 @@
 
   bestchoice.choice = A_NONE;      
   bestchoice.want   = 0;
-  bestchoice.type   = 0;
+  bestchoice.type   = CT_NONE;
 
   if( is_barbarian(pplayer) ) {    /* always build best attack unit */
     Unit_Type_id i, iunit, bestunit = -1;
@@ -207,7 +208,7 @@
     if (bestunit != -1) {
       bestchoice.choice = bestunit;
       bestchoice.want   = 101;
-      bestchoice.type   = 2;
+      bestchoice.type   = CT_ATTACKER;
     }
     else {
       freelog(LOG_VERBOSE, "Barbarians don't know what to build!\n");
@@ -260,7 +261,7 @@
       establish_city_distances(pplayer, pcity); /* for caravans in other cities */
     } else {
       pcity->currently_building = bestchoice.choice;
-      pcity->is_building_unit    = (bestchoice.type > 0);
+      pcity->is_building_unit   = is_unit_choice_type(bestchoice.type);
     }
 
     return;
@@ -330,7 +331,7 @@
       break;
 
     bestchoice.want = 0;
-    bestchoice.type = 0;
+    bestchoice.type = CT_NONE;
     bestchoice.choice = 0;
     city_list_iterate(pplayer->cities, acity)
       if (acity->anarchy) continue;
@@ -343,8 +344,12 @@
     city_list_iterate_end;
 
     if (!bestchoice.want) break;
+
+    ASSERT_REAL_CHOICE_TYPE(bestchoice.type);
  
-    if (bestchoice.type && (!frugal || bestchoice.want > 200)) { /* if we want a unit */
+    if (is_unit_choice_type(bestchoice.type) &&
+        (!frugal || bestchoice.want > 200)) { /* if we want a unit */
+
       buycost = city_buy_cost(pcity);
       unit_list_iterate(map_get_tile(pcity->x, pcity->y)->units, punit)
         id = can_upgrade_unittype(pplayer, punit->type);
@@ -401,40 +406,45 @@
         pplayer->research.researching == A_NONE) { /* nothing else to do */
       buycost = city_buy_cost(pcity);
       if (!pcity->shield_stock) ;
-      else if (!bestchoice.type && is_wonder(bestchoice.choice) &&
-               buycost >= 200) ; /* wait for more vans */
-      else if (bestchoice.type && unit_flag(bestchoice.choice, F_SETTLERS) &&
-          !city_got_effect(pcity, B_GRANARY) && (pcity->size < 2 ||
-         pcity->food_stock < pcity->size * game.foodbox)) ;
-      else if (bestchoice.type && bestchoice.type < 3 && /* not a defender */
-        buycost > unit_types[bestchoice.choice].build_cost * 2) { /* too expensive */
+      else if (bestchoice.type == CT_BUILDING &&
+               is_wonder(bestchoice.choice) &&
+               buycost >= 200); /* wait for more vans */
+
+      else if (is_unit_choice_type(bestchoice.type) &&
+               unit_flag(bestchoice.choice, F_SETTLERS) &&
+               !city_got_effect(pcity, B_GRANARY) && (pcity->size < 2 ||
+               pcity->food_stock < pcity->size * game.foodbox));
+      else if (is_unit_choice_type(bestchoice.type) &&
+               bestchoice.type != CT_DEFENDER &&
+               buycost > unit_types[bestchoice.choice].build_cost * 2) { /* too expensive */
         if (unit_flag(bestchoice.choice, F_CARAVAN) &&
             pplayer->ai.maxbuycost < 100) pplayer->ai.maxbuycost = 100;
-      }
 #ifdef GRAVEDANGERWORKS
-      else if (bestchoice.type == 3 && pcity->size == 1 &&
-        pcity->ai.grave_danger > (assess_defense_quadratic(pcity) +
-  ai_city_defender_value(pcity, U_LEGION, bestchoice.choice)) * 2 &&
+      } else if (bestchoice.type == CT_DEFENDER && pcity->size == 1 &&
+               pcity->ai.grave_danger > (assess_defense_quadratic(pcity) +
+             ai_city_defender_value(pcity, U_LEGION, bestchoice.choice)) * 2 &&
                pcity->food_stock + pcity->food_surplus < 10) { /* We're DOOMED */
 	 freelog(LOG_VERBOSE, "%s is DOOMED!", pcity->name);
          try_to_sell_stuff(pplayer, pcity); /* and don't buy stuff */
          pcity->currently_building = ai_choose_defender_limited(pcity,
                   pcity->shield_stock + pcity->shield_surplus, 0);
-      }
 #endif
-      else if ((pplayer->economic.gold-pplayer->ai.est_upkeep) >= buycost
+      } else if ((pplayer->economic.gold-pplayer->ai.est_upkeep) >= buycost
 	      && (!frugal || bestchoice.want > 200)) {
 	if (ai_fuzzy(pplayer,1) || (pcity->ai.grave_danger
 				    && !assess_defense(pcity))) {
 	  really_handle_city_buy(pplayer, pcity); /* adequately tested now */
 	}
-      } else if (bestchoice.type || !is_wonder(bestchoice.choice)) {
+      } else if (is_unit_choice_type(bestchoice.type) ||
+                 !is_wonder(bestchoice.choice)) {
 	freelog(LOG_DEBUG, "%s wants %s but can't afford to buy it"
 		      " (%d < %d).", pcity->name,
-		      (bestchoice.type ? unit_name(bestchoice.choice)
-		       : get_improvement_name(bestchoice.choice)),
-		      pplayer->economic.gold, buycost);
-        if (bestchoice.type && !unit_flag(bestchoice.choice, F_NONMIL)) {
+                (is_unit_choice_type(bestchoice.type) ?
+                   unit_name(bestchoice.choice) :
+		   get_improvement_name(bestchoice.choice)),
+		pplayer->economic.gold, buycost);
+        if (is_unit_choice_type(bestchoice.type) &&
+            !unit_flag(bestchoice.choice, F_NONMIL)) {
           if (pcity->ai.grave_danger && !assess_defense(pcity)) { /* oh dear */
             try_to_sell_stuff(pplayer, pcity);
             if ((pplayer->economic.gold-pplayer->ai.est_upkeep) >= buycost)
@@ -445,10 +455,14 @@
           } else if (buycost > pplayer->ai.maxbuycost) pplayer->ai.maxbuycost = buycost;
 /* possibly upgrade units here */
         } /* end panic subroutine */
-        if (bestchoice.type && unit_flag(bestchoice.choice, F_CARAVAN))
-            if (buycost > pplayer->ai.maxbuycost) pplayer->ai.maxbuycost = buycost;
+        if (is_unit_choice_type(bestchoice.type) &&
+            unit_flag(bestchoice.choice, F_CARAVAN)) {
+          if (buycost > pplayer->ai.maxbuycost)
+            pplayer->ai.maxbuycost = buycost;
 /* Gudy reminded me AI was slow to build wonders, I thought of the above -- Syela */
-        if (!bestchoice.type) switch (bestchoice.choice) {
+        }
+        if (bestchoice.type == CT_BUILDING) {
+          switch (bestchoice.choice) {
           case B_AQUEDUCT:
             if (city_happy(pcity)) break;
         /* PASS THROUGH */
@@ -463,7 +477,8 @@
             if (buycost > pplayer->ai.maxbuycost) pplayer->ai.maxbuycost = buycost;
             break;
 /* granaries/harbors/wonders not worth the tax increase */
-        } /* end switch */
+          } /* end switch */
+        }
 /* I just saw Alexander save up for walls then buy a granary.  Never again! -- Syela */
 /*        if (bestchoice.want > 200 && pplayer->ai.maxbuycost) frugal++; */
         if (pplayer->ai.maxbuycost) frugal++; /* much more frugal -- Syela */
diff ai/aihand.c ai/aihand.c
--- ai/aihand.c	Thu Jan 11 11:01:46 2001
+++ ai/aihand.c	Thu Jan 11 15:07:34 2001
@@ -513,3 +513,9 @@
   freelog(LOG_DEBUG, "Done with %s.", pplayer->name);
 }
 
+
+int is_unit_choice_type(enum choice_type type)
+{
+   return type == CT_NONMIL || type == CT_ATTACKER || type == CT_DEFENDER;
+}
+
diff ai/aihand.h ai/aihand.h
--- ai/aihand.h	Sat Jun 12 10:41:38 1999
+++ ai/aihand.h	Thu Jan 11 15:07:38 2001
@@ -18,4 +18,6 @@
 void ai_do_first_activities(struct player *pplayer);
 void ai_do_last_activities(struct player *pplayer);
 
+int is_unit_choice_type(enum choice_type type);
+
 #endif  /* FC__AIHAND_H */
diff ai/aitools.c ai/aitools.c
--- ai/aitools.c	Thu Jan 11 11:01:46 2001
+++ ai/aitools.c	Thu Jan 11 22:24:37 2001
@@ -169,7 +169,7 @@
   }
   choice->want = want;
   choice->choice = id;
-  choice->type = 0;
+  choice->type = CT_BUILDING;
 }
 
 
diff common/city.h common/city.h
--- common/city.h	Mon Jan  1 15:59:11 2001
+++ common/city.h	Thu Jan 11 22:49:56 2001
@@ -116,11 +116,19 @@
 }
 
 
+enum choice_type { CT_NONE = 0, CT_BUILDING = 0, CT_NONMIL, CT_ATTACKER,
+                   CT_DEFENDER, CT_LAST };
+
+
+#define ASSERT_REAL_CHOICE_TYPE(type)                        \
+        assert(type >= 0 && type < CT_LAST &&                \
+               (CT_NONE == CT_BUILDING || type != CT_NONE));
+
 
 struct ai_choice {
   int choice;            /* what the advisor wants */
   int want;              /* how bad it wants it (0-100) */
-  int type;              /* unit/building or other depending on question */
+  enum choice_type type; /* unit/building or other depending on question */
 };
 
 struct ai_city {