From 'The Guiness book of railway facts and feats'
The heaviest and longest train, with the largest number of wagons
recorded, was run on the 3'6" gauge Sishen-Saldanha railway in South
Africa on 26-27 August 1989. The train consisted of 660 wagons each
loaded to 105 tons gross, a tank car and a caboose (guards van). The
train was moved by nine 50kv electric and seven diesel electric
locomotives distributed along the train. The train was 7.3km
(4.5miles) long and weighed 69393 tons, excluding locomotives. It
travelled 861km (535 miles)
EDITED