diff --git a/biome.lisp b/biome.lisp
index 6be8217..469ca2f 100644
--- a/biome.lisp
+++ b/biome.lisp
@@ -11,9 +11,10 @@
 
 (defstruct biome
 	(name "")
-	(char #\.) ;map display character
-    (init-items '()) ;initial items for patches with this biome
-	(update-fn #'(lambda (patch-pos) NIL))) ;needs a patch position argument
+	(ground "")
+	(occupants '()) ;an alist of possible occupants and their probabilities
+	(char #\.) ;default map display character
+	(col 'white)) ;default map display colour
 
 
 (let ((biome-list NIL))
@@ -27,46 +28,35 @@
 	`(register-biome ,name
 		 (make-biome ,@body)))
 
-;; Grasslands biome
 
-(defun update-grasslands (patch-pos)
-	;;TODO
-	)
+;; Biome definitions
 
 (new-biome 'grassland
-	:name "grassland" :char #\i
-	:init-items NIL ;TODO
-	:update-fn #'update-grasslands)
-
-;; Forest biome
-
-(defun update-forest (patch-pos)
-	;;TODO
-	)
+	:name "grassland"
+	:ground "tall elephant grass"
+	:char #\; :col 'yellow
+	:occupants '((acacia 5) (boulder 1))) ;TODO
 
 (new-biome 'forest
-	:name "forest" :char #\Y
-	:init-items NIL ;TODO
-	:update-fn #'update-forest)
-
-;; Stream biome
-
-(defun update-stream (patch-pos)
-	;;TODO
-	)
+	:name "forest"
+	:ground "leaf litter and small shrubs"
+	:char #\. :col 'green
+	:occupants '((miombo 20) (acacia 10))) ;TODO
 
 (new-biome 'stream
-	:name "stream" :char #\~
-	:init-items NIL ;TODO
-	:update-fn #'update-stream)
+	:name "stream"
+	:ground "shallow flowing water"
+	:char #\~ :col 'blue
+	:occupants '()) ;TODO
 
-;; Hill biome
-
-(defun update-hill (patch-pos)
-	;;TODO
-	)
+(new-biome 'swamp
+	:name "swamp"
+	:ground "short sedge grass growing on boggy black soil"
+	:char #\w :col 'green
+	:occupants '()) ;TODO
 
 (new-biome 'hill
-	:name "hill" :char #\m
-	:init-items NIL ;TODO
-	:update-fn #'update-hill)
+	:name "hill"
+	:ground "hard, stony soil"
+	:char #\m :col 'white
+	:occupants '((boulder 15))) ;TODO

diff --git a/biome.lisp b/biome.lisp
index 6be8217..469ca2f 100644
--- a/biome.lisp
+++ b/biome.lisp
@@ -11,9 +11,10 @@
 
 (defstruct biome
 	(name "")
-	(char #\.) ;map display character
-    (init-items '()) ;initial items for patches with this biome
-	(update-fn #'(lambda (patch-pos) NIL))) ;needs a patch position argument
+	(ground "")
+	(occupants '()) ;an alist of possible occupants and their probabilities
+	(char #\.) ;default map display character
+	(col 'white)) ;default map display colour
 
 
 (let ((biome-list NIL))
@@ -27,46 +28,35 @@
 	`(register-biome ,name
 		 (make-biome ,@body)))
 
-;; Grasslands biome
 
-(defun update-grasslands (patch-pos)
-	;;TODO
-	)
+;; Biome definitions
 
 (new-biome 'grassland
-	:name "grassland" :char #\i
-	:init-items NIL ;TODO
-	:update-fn #'update-grasslands)
-
-;; Forest biome
-
-(defun update-forest (patch-pos)
-	;;TODO
-	)
+	:name "grassland"
+	:ground "tall elephant grass"
+	:char #\; :col 'yellow
+	:occupants '((acacia 5) (boulder 1))) ;TODO
 
 (new-biome 'forest
-	:name "forest" :char #\Y
-	:init-items NIL ;TODO
-	:update-fn #'update-forest)
-
-;; Stream biome
-
-(defun update-stream (patch-pos)
-	;;TODO
-	)
+	:name "forest"
+	:ground "leaf litter and small shrubs"
+	:char #\. :col 'green
+	:occupants '((miombo 20) (acacia 10))) ;TODO
 
 (new-biome 'stream
-	:name "stream" :char #\~
-	:init-items NIL ;TODO
-	:update-fn #'update-stream)
+	:name "stream"
+	:ground "shallow flowing water"
+	:char #\~ :col 'blue
+	:occupants '()) ;TODO
 
-;; Hill biome
-
-(defun update-hill (patch-pos)
-	;;TODO
-	)
+(new-biome 'swamp
+	:name "swamp"
+	:ground "short sedge grass growing on boggy black soil"
+	:char #\w :col 'green
+	:occupants '()) ;TODO
 
 (new-biome 'hill
-	:name "hill" :char #\m
-	:init-items NIL ;TODO
-	:update-fn #'update-hill)
+	:name "hill"
+	:ground "hard, stony soil"
+	:char #\m :col 'white
+	:occupants '((boulder 15))) ;TODO
diff --git a/terranostra.lisp b/terranostra.lisp
index 7771626..917698b 100644
--- a/terranostra.lisp
+++ b/terranostra.lisp
@@ -19,12 +19,11 @@
 	(pos '(0 0)) ;position
 	(biome (get-biome 'grassland))
 	(items '())
-	(animals '()))
+	(occupant NIL))
 
 
 (defun init-matrix (size)
 	"Create a square matrix of empty patches"
-	(format t "~&Creating a ~Sx~S world matrix." size size)
 	(do ((y 0 (1+ y)) (world NIL) (row NIL NIL))
 		((= y size) world)
 		(dotimes (x size)