imageArray = new Array('arch_1.jpg','arch_2.jpg','arch_3.jpg','arch_4.jpg','arch_5.jpg','arch_6.jpg','arch_7.jpg','arch_8.jpg', 'arch_9.jpg','arch_10.jpg','arch_11.jpg','arch_12.jpg','arch_13.jpg');
var totalImages = imageArray.length;

function switchImage(currentImageIndex) {
	if (currentImageIndex == totalImages - 1) {
		currentImageIndex = 0;
	} else {
		currentImageIndex = currentImageIndex + 1;
	}
	img = document.getElementById('arch');
	img.style.background = "url(images/" + imageArray[currentImageIndex] + ")";
	var recur_call = "switchImage(" + currentImageIndex + ")";
	timerID = setTimeout(recur_call, 2500);
}