In the Middle Ages large organs were built in the huge Gothic cathedrals in Britain. These instruments did not have different stops: all the ranks sounded at once. They were played by a slider mechanism. Only in the 11th, 12th and 13th centuries did they start to use a keyboard. The so-called "Mixture Organ" (or "Blockwerk") still sounded several pitches at once. Very small organs called "portatives" (because they could be carried) were used in . "Positives" were a bit bigger and were used to accompany singing in the church. The "Regal" was like a portative but it had reeds and no pipes. It could be put on a table. The world's oldest organ is generally agreed to be the one built at Sion, Switzerland in the 15th century. the organ.