There were actually three different Jerichos throughout its long history.
Old Testament Jericho is generally identified with the mound of Tell esSultan, about 2 kilometers (a little more than a mile) from the village of er-Riha. This village is modern Jericho, located about 27 kilometers (17 miles) northeast of Jerusalem. New Testament Jericho is identified with the mounds of Tulul Abu el-'Alayiq, about 2 kilometers (a little more than a mile) west of modern Jericho and south of Old Testament Jericho.
By far the most imposing site of the three is Old Testament Jericho, a pear-shaped mound about 366 meters (400 yards) long, north to south, 183 meters (200 yards) wide at the north end, and some 67 meters (70 yards) high. It has been the site of numerous archaeological diggings and is a favorite stop for Holy Land tourists.
From 1907 until 1911, the German scholars Ernst Sellin and Carl Watzinger excavated this site. But it was the British archaeologist John Garstang whose excavations from 1930 to 1936 yielded significant information. Garstang believed he had found ample evidence of Joshua's destruction of the city. He discovered an inner wall about 3.66 meters (12 feet) thick and an outer wall about 1.83 meters (6 feet) thick. Garstang was convinced that he had found the fabled walls of Jericho.
(from Nelson's Illustrated Bible Dictionary, Copyright (c)1986, Thomas Nelson Publishers)