diff --git a/mkdocs/config/config_options.py b/mkdocs/config/config_options.py
index d96999016a..8caf16ad5e 100644
--- a/mkdocs/config/config_options.py
+++ b/mkdocs/config/config_options.py
@@ -193,21 +193,33 @@ class Deprecated(BaseConfigOption):
     ConfigOption instance, then the value is validated against that type.
     """
 
-    def __init__(self, moved_to=None, message='', option_type=None):
+    def __init__(self, moved_to=None, message=None, removed=False, option_type=None):
         super().__init__()
         self.default = None
         self.moved_to = moved_to
-        self.message = message or (
-            'The configuration option {} has been deprecated and '
-            'will be removed in a future release of MkDocs.'
-        )
+        if not message:
+            if removed:
+                message = "The configuration option '{}' was removed from MkDocs."
+            else:
+                message = (
+                    "The configuration option '{}' has been deprecated and "
+                    "will be removed in a future release of MkDocs."
+                )
+            if moved_to:
+                message += f" Use '{moved_to}' instead."
+
+        self.message = message
+        self.removed = removed
         self.option = option_type or BaseConfigOption()
+
         self.warnings = self.option.warnings
 
     def pre_validation(self, config, key_name):
         self.option.pre_validation(config, key_name)
 
         if config.get(key_name) is not None:
+            if self.removed:
+                raise ValidationError(self.message.format(key_name))
             self.warnings.append(self.message.format(key_name))
 
             if self.moved_to is not None:
@@ -566,16 +578,6 @@ def _repr_item(cls, value):
         else:
             return f"a {type(value).__name__}: {value!r}"
 
-    def post_validation(self, config, key_name):
-        # TODO: remove this when `pages` config setting is fully deprecated.
-        if key_name == 'pages' and config['pages'] is not None:
-            if config['nav'] is None:
-                # copy `pages` config to new 'nav' config setting
-                config['nav'] = config['pages']
-            warning = ("The 'pages' configuration option has been deprecated and will "
-                       "be removed in a future release of MkDocs. Use 'nav' instead.")
-            self.warnings.append(warning)
-
 
 class Private(OptionallyRequired):
     """
diff --git a/mkdocs/config/defaults.py b/mkdocs/config/defaults.py
index b3f6ebca02..95d3c44095 100644
--- a/mkdocs/config/defaults.py
+++ b/mkdocs/config/defaults.py
@@ -20,8 +20,7 @@ def get_schema():
 
         # Defines the structure of the navigation.
         ('nav', config_options.Nav()),
-        # TODO: remove this when the `pages` config setting is fully deprecated.
-        ('pages', config_options.Nav()),
+        ('pages', config_options.Deprecated(removed=True, moved_to='nav')),
 
         # The full URL to where the documentation will be hosted
         ('site_url', config_options.URL(is_dir=True)),
diff --git a/mkdocs/tests/config/config_options_tests.py b/mkdocs/tests/config/config_options_tests.py
index 2dd93b389a..db01ba7869 100644
--- a/mkdocs/tests/config/config_options_tests.py
+++ b/mkdocs/tests/config/config_options_tests.py
@@ -125,6 +125,11 @@ def test_deprecated_option_with_invalid_type(self):
         with self.assertRaises(config_options.ValidationError):
             option.validate(config['d'])
 
+    def test_removed_option(self):
+        option = config_options.Deprecated(removed=True, moved_to='foo')
+        with self.assertRaises(config_options.ValidationError):
+            option.pre_validation({'d': 'value'}, 'd')
+
     def test_deprecated_option_with_type_undefined(self):
         option = config_options.Deprecated(option_type=config_options.Type(str))
         option.validate(None)
diff --git a/mkdocs/tests/config/config_tests.py b/mkdocs/tests/config/config_tests.py
index f20b1a81ec..295a9bd492 100644
--- a/mkdocs/tests/config/config_tests.py
+++ b/mkdocs/tests/config/config_tests.py
@@ -61,13 +61,13 @@ def test_config_option(self):
         """
         expected_result = {
             'site_name': 'Example',
-            'pages': [
+            'nav': [
                 {'Introduction': 'index.md'}
             ],
         }
         file_contents = dedent("""
         site_name: Example
-        pages:
+        nav:
         - 'Introduction': 'index.md'
         """)
         with TemporaryDirectory() as temp_path:
@@ -81,7 +81,7 @@ def test_config_option(self):
 
             result = config.load_config(config_file=config_file.name)
             self.assertEqual(result['site_name'], expected_result['site_name'])
-            self.assertEqual(result['pages'], expected_result['pages'])
+            self.assertEqual(result['nav'], expected_result['nav'])
 
     def test_theme(self):
         with TemporaryDirectory() as mytheme, TemporaryDirectory() as custom:
@@ -219,28 +219,19 @@ def test_empty_nav(self):
         conf.validate()
         self.assertEqual(conf['nav'], None)
 
-    def test_copy_pages_to_nav(self):
-        # TODO: remove this when pages config setting is fully deprecated.
+    def test_error_on_pages(self):
         conf = config.Config(schema=defaults.get_schema())
         conf.load_dict({
             'site_name': 'Example',
             'pages': ['index.md', 'about.md'],
-            'config_file_path': os.path.join(os.path.abspath('.'), 'mkdocs.yml')
-        })
-        conf.validate()
-        self.assertEqual(conf['nav'], ['index.md', 'about.md'])
-
-    def test_dont_overwrite_nav_with_pages(self):
-        # TODO: remove this when pages config setting is fully deprecated.
-        conf = config.Config(schema=defaults.get_schema())
-        conf.load_dict({
-            'site_name': 'Example',
-            'pages': ['index.md', 'about.md'],
-            'nav': ['foo.md', 'bar.md'],
-            'config_file_path': os.path.join(os.path.abspath('.'), 'mkdocs.yml')
         })
-        conf.validate()
-        self.assertEqual(conf['nav'], ['foo.md', 'bar.md'])
+        errors, warnings = conf.validate()
+        self.assertEqual(warnings, [])
+        self.assertEqual(len(errors), 1)
+        self.assertEqual(
+            str(errors[0][1]),
+            "The configuration option 'pages' was removed from MkDocs. Use 'nav' instead."
+        )
 
     def test_doc_dir_in_site_dir(self):