The earliest fortifications yet discovered date from 7000 B.C., but evidence of siege weapons doesn't appear until much later. We can assume, however, that siege equipment was in use long before the first evidence that has survived. Evidence of a scaling ladder does not appear until about 2500 B.C. The earliest record of a simple battering ram comes from 1900 B.C. A more powerful ram plus the undermining of walls appears by 880 B.C. The mobile siege tower first appears one hundred years later. The catapult was invented by Greeks in 397 B.C. There were no further significant advances in siege engines until the advent of gunpowder.