I encountered the following error with a root cause of Module 'ngRoute' is not available

Uncaught Error: [$injector:modulerr] Failed to instantiate module
Amail due to:

Error: [$injector:modulerr] Failed to instantiate module ngRoute due
to:

Error: [$injector:nomod] Module 'ngRoute' is not available! You either
misspelled the module name or forgot to load it. If registering a
module ensure that you specify the dependencies as the second
argument.

Javascript code :

var amailServices = angular.module('Amail',['ngRoute']);

function emailRouteConfig($routeProvider) {

$routeProvider.

    when('/', {

        controller: ListController,

        templateUrl : 'list.html'}).



    when('/view/:id',{

        controller : DetailsController,

        templateUrl:'detail.html'}).



    otherwise({

        redirectTo:'/'

    });

}

amailServices.config(emailRouteConfig);

How to fix this