Edit in JSFiddle

JavaScript
HTML
CSS
Result

var map;
var cityCircle;
function initialize()
{
    map = new google.maps.Map(document.getElementById("map_canvas"),
    {
        zoom: 7,
        center: new google.maps.LatLng(18.4894, 73.910158),
    mapTypeId: google.maps.MapTypeId.TERRAIN
    });
    
    cityCircle = new google.maps.Circle(
    {
    map: map,
    center: new google.maps.LatLng(18.4894, 73.910158),
    radius: 100000,
    strokeColor: "#FF0000",
    fillColor: "#FF0000",
    fillOpacity: 0.35,
    });
}

<html>
<head>
<title>Google Maps API v3 Example: Circle</title>
<script type="text/javascript" src="http://maps.googleapis.com/maps/api/js?sensor=false"></script>
<script type="text/javascript">
    <!-- Copy the javascript code here in case you are trying out this code -->
</script>
</head>
<body onload="initialize()">
<div id="map_canvas" style="height: 300px; width:500px"></div>
</body>
</html>