diff --git a/src/main/java/com/ericbouchut/learndev/common/config/SecurityConfig.java b/src/main/java/com/ericbouchut/learndev/common/config/SecurityConfig.java
index 46efbe9..4320970 100644
--- a/src/main/java/com/ericbouchut/learndev/common/config/SecurityConfig.java
+++ b/src/main/java/com/ericbouchut/learndev/common/config/SecurityConfig.java
@@ -1,7 +1,9 @@
 package com.ericbouchut.learndev.common.config;
 
+import jakarta.servlet.DispatcherType;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.security.config.annotation.method.configuration.EnableMethodSecurity;
 import org.springframework.security.config.annotation.web.builders.HttpSecurity;
 import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
 import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
@@ -10,6 +12,8 @@
 
 @Configuration
 @EnableWebSecurity
+// Enables @PreAuthorize for service-level rules (e.g. course ownership).
+@EnableMethodSecurity
 public class SecurityConfig {
 
     @Bean
@@ -21,7 +25,13 @@ public PasswordEncoder passwordEncoder() {
     public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
         http
             .authorizeHttpRequests(auth -> auth
+                // The ERROR dispatch renders templates/error/*.html for a
+                // response already authorized (or denied) on its way in.
+                .dispatcherTypeMatchers(DispatcherType.ERROR).permitAll()
                 .requestMatchers("/", "/privacy", "/auth/**", "/css/**", "/js/**", "/fonts/**").permitAll()
+                .requestMatchers("/instructor/**").hasRole("INSTRUCTOR")
+                .requestMatchers("/admin/**").hasRole("ADMIN")
+                .requestMatchers("/courses/**").authenticated()
                 .anyRequest().authenticated())
             .formLogin(form -> form
                 .loginPage("/auth/login")            // GET: show the login form
diff --git a/src/main/resources/templates/error/403.html b/src/main/resources/templates/error/403.html
new file mode 100644
index 0000000..c3f70ba
--- /dev/null
+++ b/src/main/resources/templates/error/403.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html lang="en" xmlns:th="http://www.thymeleaf.org">
+<head th:replace="~{fragments/layout :: head('Access denied — learn-dev')}"></head>
+<body>
+  <th:block th:replace="~{fragments/layout :: header(null)}"></th:block>
+
+  <main class="site-main site-main--narrow" id="main" tabindex="-1">
+    <h1>Access denied</h1>
+    <p>You do not have permission to view this page.</p>
+    <p>
+      <a class="button button--primary" th:href="@{/dashboard}">Back to your dashboard</a>
+    </p>
+  </main>
+
+  <th:block th:replace="~{fragments/layout :: footer}"></th:block>
+</body>
+</html>
diff --git a/src/main/resources/templates/error/404.html b/src/main/resources/templates/error/404.html
new file mode 100644
index 0000000..a040255
--- /dev/null
+++ b/src/main/resources/templates/error/404.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html lang="en" xmlns:th="http://www.thymeleaf.org">
+<head th:replace="~{fragments/layout :: head('Page not found — learn-dev')}"></head>
+<body>
+  <th:block th:replace="~{fragments/layout :: header(null)}"></th:block>
+
+  <main class="site-main site-main--narrow" id="main" tabindex="-1">
+    <h1>Page not found</h1>
+    <p>The page you are looking for does not exist or has moved.</p>
+    <p>
+      <a class="button button--primary" th:href="@{/}">Back to the home page</a>
+    </p>
+  </main>
+
+  <th:block th:replace="~{fragments/layout :: footer}"></th:block>
+</body>
+</html>
diff --git a/src/main/resources/templates/error/500.html b/src/main/resources/templates/error/500.html
new file mode 100644
index 0000000..15b14f9
--- /dev/null
+++ b/src/main/resources/templates/error/500.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html lang="en" xmlns:th="http://www.thymeleaf.org">
+<head th:replace="~{fragments/layout :: head('Something went wrong — learn-dev')}"></head>
+<body>
+  <th:block th:replace="~{fragments/layout :: header(null)}"></th:block>
+
+  <main class="site-main site-main--narrow" id="main" tabindex="-1">
+    <h1>Something went wrong</h1>
+    <p>An unexpected error occurred on our side. Please try again in a moment.</p>
+    <p>
+      <a class="button button--primary" th:href="@{/}">Back to the home page</a>
+    </p>
+  </main>
+
+  <th:block th:replace="~{fragments/layout :: footer}"></th:block>
+</body>
+</html>
diff --git a/src/main/resources/templates/fragments/layout.html b/src/main/resources/templates/fragments/layout.html
index 3a97133..3dceece 100644
--- a/src/main/resources/templates/fragments/layout.html
+++ b/src/main/resources/templates/fragments/layout.html
@@ -4,7 +4,8 @@
   - head(title): document head with the design stylesheets
   - header(current): skip link + banner + auth-aware navigation;
     `current` names the nav entry of the calling page ('home', 'login',
-    'register', 'dashboard' or null) and drives aria-current="page"
+    'register', 'dashboard', 'instructor', 'admin' or null) and drives
+    aria-current="page"
   - footer: site footer
   Each page keeps its own <html lang> (privacy.html is lang="fr").
 -->
@@ -38,6 +39,12 @@
           <ul class="nav__list" sec:authorize="isAuthenticated()">
             <li><a class="nav__link" th:href="@{/dashboard}"
                    th:attr="aria-current=${current == 'dashboard'} ? 'page' : null">Dashboard</a></li>
+            <li sec:authorize="hasRole('INSTRUCTOR')">
+              <a class="nav__link" th:href="@{/instructor/courses}"
+                 th:attr="aria-current=${current == 'instructor'} ? 'page' : null">Instructor</a></li>
+            <li sec:authorize="hasRole('ADMIN')">
+              <a class="nav__link" th:href="@{/admin/users}"
+                 th:attr="aria-current=${current == 'admin'} ? 'page' : null">Admin</a></li>
             <li>
               <form th:action="@{/auth/logout}" method="post">
                 <button class="button button--ghost" type="submit">Log out</button>
diff --git a/src/test/java/com/ericbouchut/learndev/common/config/SecurityMatrixTest.java b/src/test/java/com/ericbouchut/learndev/common/config/SecurityMatrixTest.java
new file mode 100644
index 0000000..bb12d74
--- /dev/null
+++ b/src/test/java/com/ericbouchut/learndev/common/config/SecurityMatrixTest.java
@@ -0,0 +1,89 @@
+package com.ericbouchut.learndev.common.config;
+
+import com.ericbouchut.learndev.support.AbstractPostgresIT;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.security.test.context.support.WithMockUser;
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.redirectedUrlPattern;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+/**
+ * Access matrix for the role-gated URL prefixes: anonymous users are sent to
+ * the login page, the wrong role is denied (403), and the right role passes
+ * the gate. The instructor and admin controllers do not exist yet, so "passes
+ * the gate" is asserted as 404 (the request reached MVC dispatch); tighten
+ * those assertions to 200 as each feature phase lands.
+ *
+ * <p>Named with the {@code Test} suffix (not {@code IT}) so Surefire runs it
+ * as part of {@code mvn test}; this project does not use the Failsafe plugin.
+ */
+@SpringBootTest(properties = {
+        // This feature does not use MongoDB; keep the test context Postgres-only.
+        "spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,"
+                + "org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration"
+})
+@AutoConfigureMockMvc
+class SecurityMatrixTest extends AbstractPostgresIT {
+
+    @Autowired
+    MockMvc mvc;
+
+    // Anonymous: every gated prefix redirects to the login page.
+
+    @Test
+    void anonymous_is_redirected_to_login_on_gated_prefixes() throws Exception {
+        for (String path : new String[] {"/courses", "/instructor/courses", "/admin/users"}) {
+            mvc.perform(get(path))
+                    .andExpect(status().is3xxRedirection())
+                    .andExpect(redirectedUrlPattern("**/auth/login"));
+        }
+    }
+
+    // Student: may pass the /courses gate, denied on instructor and admin.
+
+    @Test
+    @WithMockUser(roles = "STUDENT")
+    void student_passes_courses_gate() throws Exception {
+        mvc.perform(get("/courses")).andExpect(status().isNotFound());
+    }
+
+    @Test
+    @WithMockUser(roles = "STUDENT")
+    void student_is_denied_instructor_and_admin() throws Exception {
+        mvc.perform(get("/instructor/courses")).andExpect(status().isForbidden());
+        mvc.perform(get("/admin/users")).andExpect(status().isForbidden());
+    }
+
+    // Instructor: may pass the /instructor gate, denied on admin.
+
+    @Test
+    @WithMockUser(roles = "INSTRUCTOR")
+    void instructor_passes_instructor_gate() throws Exception {
+        mvc.perform(get("/instructor/courses")).andExpect(status().isNotFound());
+    }
+
+    @Test
+    @WithMockUser(roles = "INSTRUCTOR")
+    void instructor_is_denied_admin() throws Exception {
+        mvc.perform(get("/admin/users")).andExpect(status().isForbidden());
+    }
+
+    // Admin: may pass the /admin gate; not an instructor, so denied there.
+
+    @Test
+    @WithMockUser(roles = "ADMIN")
+    void admin_passes_admin_gate() throws Exception {
+        mvc.perform(get("/admin/users")).andExpect(status().isNotFound());
+    }
+
+    @Test
+    @WithMockUser(roles = "ADMIN")
+    void admin_is_denied_instructor() throws Exception {
+        mvc.perform(get("/instructor/courses")).andExpect(status().isForbidden());
+    }
+}
