These are parallel channels in pairs or groups found in San Gwann, San Pawl Tat-Targa* Naxxar and Rabat/Dingli. It is still a mystery why and how they were constructed but it is thought the purpose was to transport heavy rocks. Some lead to the sea, to cliff edges and carry on under the sea. San Gwann is between Naxxar and Sliema. They are popularily known as Clapham Junction. Malta has most of these ruts of the whole world. www.cartrutsmalta.com is a fascinating site that attempts to solve the mystery.