The original center of Petersburg's development occurred in the low land near the river and along Old Street, which continued westward as Grove Avenue. The streets paralleling the railroad line adjacent to the Appomattox River have retained a mix of residential, commercial, and industrial functions. By the mid-nineteenth century, Petersburg had become a major regional transportation center and along with the extensive routes of the Appomattox Canal Company, a web of five rail lines spread out from the city. However, each line was deliberately constructed so as not to connect with any of the other lines. Consequently, goods and passengers had to be unloaded and reloaded at Petersburg before continuing on. Under the leadership of William Mahone, three lines merged in 1871 to become the Atlantic, Mississippi and Ohio (AM&O). When asked what AM&O stood for, Mahone replied, “All Mine and Otelia's” (his wife). The former AM&O's Italianate brick depot has a two-story central block with a cupola that accommodated passengers on the first floor and offices on the second. During the Union occupation of Petersburg, the depot was used by the quartermaster's department and later served as Mahone's office and headquarters for the Readjusters. The central entrance is flanked by two stories of round-arched double-height windows. Originally the depot had one-story wings fifteen or so bays long but the tornado of 1993 considerably clipped them.