Abstract: The kiln operating according to the parallel-flow-regenerative process has two shafts (2, 3), which at the transition from the burning zone (14) to the cooling zone (15) have a widening forming an inner step (38) at which the combustion gases are transferred to the adjacent shaft (2, 3). This widened shaft area continues at least approximately cylindrically up to the bottom opening ( 35 ) of the shafts ( 2, 3 ) closed by a discharge device ( 34 ). This design of the shaft areas makes it possible, preferably together with an improved fuel distribution and charging device and in the case of satisfactory product quality, to burn limestone having particles in the size range 10 to 30 mm, which could hitherto not be burned in shaft kilns.