The William E. Gordon Telescope at the Arecibo Observatory in Puerto Rico was the second largest radio telescope in the world at the time of its collapse in December 2020. The telescope had a 305-meter diameter spherical primary reflector, the size of 3 football fields, and could illuminate approximately 225 meters at a time. The spherical aberration correction was done using its secondary optics in the Gregorian dome. Given the enormous collecting area and the extensive observing frequency coverage, from 327 MHz to 10 GHz, with a 2-millimeter surface accuracy, the Arecibo Telescope was the most sensitive radio telescope in the world. Due to its size, the timing observations of pulsars obtained with the Arecibo Telescope were more sensitive than those with the GBT. The Arecibo Telescope was one of the primary instruments in pulsar searching, leading to the discovery of many pulsars, including highly stable millisecond pulsars that were ideal for NANOGrav-type sciences. The dish was so large and had to remain fixed on the ground, while the Gregorian dome could move in position with a limited capability. This led the Arecibo Telescope to access only a part of the sky with a range of 40 degrees in declination directly overhead the telescope.