diff -ur -X diff_ignore freeciv-cvs/common/unit.c freeciv-modified/common/unit.c
--- freeciv-cvs/common/unit.c	Sat Dec 16 00:51:45 2000
+++ freeciv-modified/common/unit.c	Fri Jan 19 21:58:43 2001
@@ -708,7 +708,7 @@
     return 0;

   case ACTIVITY_FORTRESS:
-    return (unit_flag(punit->type, F_SETTLERS) &&
+    return (!map_get_tile(punit->x,punit->y)->city && unit_flag(punit->type, F_SETTLERS) &&
 	    player_knows_techs_with_flag(pplayer, TF_FORTRESS) &&
 	    !(ptile->special&S_FORTRESS) && ptile->terrain!=T_OCEAN);