The Victorian era in particular became notorious for the conditions under which children were employed. Children as young as four were employed in production factories and mines working long hours in dangerous, often fatal, working conditions. In coal mines, children would crawl through tunnels too narrow and low for adults. Children also worked as errand boys, crossing sweepers, shoe blacks, or selling matches, flowers and other cheap goods. Some children undertook work as apprentices to respectable trades, such as building or as domestic servants (there were over 120,000 domestic servants in London in the mid-18th century). Working hours were long: builders worked 64 hours a week in summer and 52 in winter, while domestic servants worked 80-hour weeks.