some time in may 640 ad, 'amr sent a detachment to raid the city of fayoum. the byzantines had anticipated this and had therefore strongly guarded the roads leading to the city. they had also fortified their garrison in the nearby town of lahun. when the muslim arabs realized that fayoum was too strong for them to invade, they headed towards the western desert, where they looted all the cattle and animals they could. they subsequently headed to oxyrhynchus (per-medjed), which was defeated. the arabs then returned to lower egypt down the river nile.