In addition to small pedestrian postern gates like the one by Tower Hill, it had four main gates: Bishopsgate and Aldgate in the northeast at the roads to Eboracum (York) and to Camulodunum (Colchester) and Newgate and Ludgate in the west along at the road that divided for travel to Viroconium (Wroxeter) and to Calleva (Silchester) and at another road that ran along the Thames to the city's main cemetery and the old ford at Westminster. The wall partially utilized the army's existing fort, strengthening its outer wall with a second course of stone to match the rest of the course. The fort had two gates of its own—Cripplegate to the north and another to the west—but these were not along major roads. Aldersgate was eventually added, perhaps to replace the west gate of the fort. (The names of all these gates are medieval, as they continued to be occasionally refurbished and replaced until their demolition in the 17th and 18th centuries to permit widening the roads.) The wall initially left the riverbank undefended: this was corrected in the 3rd century.