You have probably seen the very earliest of photographs made by people like Henry Fox Talbot and Neipce. They often showed urban scenes completely devoid of human presence. this was not by design but due to the fact that the speed of the emulsion used was equivalent of 1/2 to 2 asa. Coupled with probably some very small apertures for a large plate camera and you had exposures hours long.

Interestingly enough, I was browsing through the most resent issue of Camera Arts at the book store and there was an article about Chip Foreli (sp) and some of his techniques. One image he used a ND filter to reduce exposure by 13(&#33 stops. He was trying to get a night time effect during the daytime. I don't recall the exact length of the exposure but it was probably several minutes. I would imagine that would eliminate any moving people from recording on the film.