diff --git a/lib/rage-rb.rb b/lib/rage-rb.rb
index 96b30012..76131079 100644
--- a/lib/rage-rb.rb
+++ b/lib/rage-rb.rb
@@ -7,7 +7,25 @@
 
 module Rage
   def self.application
-    Application.new(__router)
+    app = Application.new(__router)
+
+    config.middleware.middlewares.reverse.inject(app) do |next_in_chain, (middleware, args, block)|
+      # in Rails compatibility mode we first check if the middleware is a part of the Rails middleware stack;
+      # if it is - it is expected to be built using `ActionDispatch::MiddlewareStack::Middleware#build`
+      if Rage.config.internal.rails_mode
+        rails_middleware = Rails.application.config.middleware.middlewares.find { |m| m.name == middleware.name }
+      end
+
+      if rails_middleware
+        rails_middleware.build(next_in_chain)
+      else
+        middleware.new(next_in_chain, *args, &block)
+      end
+    end
+  end
+
+  def self.multi_application
+    Rage::Router::Util::Cascade.new(application, Rails.application)
   end
 
   def self.routes
@@ -43,28 +61,8 @@ def self.logger
     @logger ||= config.logger
   end
 
-  def self.load_middlewares(rack_builder)
-    config.middleware.middlewares.each do |middleware, args, block|
-      # in Rails compatibility mode we first check if the middleware is a part of the Rails middleware stack;
-      # if it is - it is expected to be built using `ActionDispatch::MiddlewareStack::Middleware#build`, but Rack
-      # expects the middleware to respond to `#new`, so we wrap the middleware into a helper module
-      if Rage.config.internal.rails_mode
-        rails_middleware = Rails.application.config.middleware.middlewares.find { |m| m.name == middleware.name }
-        if rails_middleware
-          wrapper = Module.new do
-            extend self
-            attr_accessor :middleware
-            def new(app, *, &)
-              middleware.build(app)
-            end
-          end
-          wrapper.middleware = rails_middleware
-          middleware = wrapper
-        end
-      end
-
-      rack_builder.use(middleware, *args, &block)
-    end
+  def self.load_middlewares(_)
+    puts "`Rage.load_middlewares` is deprecated and has been merged into `Rage.application`. Please remove this call."
   end
 
   def self.code_loader
diff --git a/lib/rage/router/backend.rb b/lib/rage/router/backend.rb
index 6979e92a..7dcd6d45 100644
--- a/lib/rage/router/backend.rb
+++ b/lib/rage/router/backend.rb
@@ -68,12 +68,18 @@ def on(method, path, handler, constraints: {}, defaults: nil)
       raise "Invalid route handler format, expected to match the 'controller#action' pattern" unless handler =~ STRING_HANDLER_REGEXP
 
       controller, action = Rage::Router::Util.path_to_class($1), $2
-      run_action_method_name = controller.__register_action(action.to_sym)
 
-      meta[:controller] = $1
-      meta[:action] = $2
+      if controller.ancestors.include?(RageController::API)
+        run_action_method_name = controller.__register_action(action.to_sym)
 
-      handler = eval("->(env, params) { #{controller}.new(env, params).#{run_action_method_name} }")
+        meta[:controller] = $1
+        meta[:action] = $2
+
+        handler = eval("->(env, params) { #{controller}.new(env, params).#{run_action_method_name} }")
+      else
+        # this is a Rails controller; notify `Rage::Router::Util::Cascade` to forward the request to Rails
+        handler = ->(_, _) { [404, { "X-Cascade" => "pass" }, []] }
+      end
     else
       raise "Non-string route handler should respond to `call`" unless handler.respond_to?(:call)
       # while regular handlers are expected to be called with the `env` and `params` objects,
diff --git a/lib/rage/router/util.rb b/lib/rage/router/util.rb
index 929d630e..9c9527b6 100644
--- a/lib/rage/router/util.rb
+++ b/lib/rage/router/util.rb
@@ -30,4 +30,19 @@ def path_to_name(str)
       end
     end
   end
+
+  # @private
+  class Cascade
+    def initialize(rage_app, rails_app)
+      @rage_app = rage_app
+      @rails_app = rails_app
+    end
+
+    def call(env)
+      result = @rage_app.call(env)
+      return result if result[0] == :__http_defer__ || result[1]["X-Cascade".freeze] != "pass".freeze
+
+      @rails_app.call(env)
+    end
+  end
 end
diff --git a/lib/rage/templates/config.ru b/lib/rage/templates/config.ru
index 52de8a40..049a1ad5 100644
--- a/lib/rage/templates/config.ru
+++ b/lib/rage/templates/config.ru
@@ -1,4 +1,3 @@
 require_relative "config/application"
 
 run Rage.application
-Rage.load_middlewares(self)
diff --git a/spec/integration/test_app/config.ru b/spec/integration/test_app/config.ru
index 52de8a40..049a1ad5 100644
--- a/spec/integration/test_app/config.ru
+++ b/spec/integration/test_app/config.ru
@@ -1,4 +1,3 @@
 require_relative "config/application"
 
 run Rage.application
-Rage.load_middlewares(self)
diff --git a/spec/rspec/config.ru b/spec/rspec/config.ru
index f8774ed1..279ddd62 100644
--- a/spec/rspec/config.ru
+++ b/spec/rspec/config.ru
@@ -1,2 +1 @@
 run Rage.application
-Rage.load_middlewares(self)