Old lavatories have always interested me - I once wrote a book about them (an encycloopaedia) - and I am delighted to say that as part of my forthcoming tv series about ancient technology I have had the chance to get acquainted with some of the oldest loos on earth. The archaeological evidence is that people started making solid lavatories with proper drains more than 4000 years ago.

At Mohenjo Daro, in the north-west of the Indian subcontinent, the Harrapan people built a large city with broad streets laid out in a grid system - an amazing example of town planning from about 2300 BC. In one corner of each house there was a small room with a primitive shower, and a lavatory with a wooden seat. A drain below it carried the effluent out through the wall into the main sewer under the road. These brick-built sewers were a metre or two below ground, two metres deep, and equipped with cess-pits, soakaways, and manholes with inspection covers.

On the island of Crete, in the south-east corner of the  Mediterranean, the Minoan civilization was flourishing around 1500 BC, and according to legend the great engineer Daedalus built a fabulous palace at Knossos for King Minos. The palace boasted a superb marble lavatory with a wooden seat and a flushing system. I went on a pilgrimage to see the remains of the great palace, but unfortunately, because of earthquake damage, the building with the lavatory has been 'temporarily' closed for the last ten years.

The grandfather of all lavatory sites is at Skara Brae on the west coast of the mainland of Orkney, just north of Scotland. Here a great storm in 1850 ripped the turf off the sand dunes, exposing a stone-age estate of about ten little houses, built some 5000 years ago. Each consists of just one room, with a great stone dresser opposite the door, a big bed on the right and a small one on the left, and a fireplace in the middle. In the corner of each little house is a tiny alcove, with a hole in the ground that drops straight into a system of interconnecting drains that lead down towards the sea. These are - as far as we know - the oldest lavatories in the world, and I was excited at the chance to visit them just a few weeks ago.