NUSearch, Northwestern University Library's search tool, can be used to find books and other library resources. To search for books, it is best to click on the "Books, Images, & More" tab; otherwise, you are likely to be overwhelmed with articles.
Rome AND Trade
(Rome OR "Roman Empire") AND "grain trade"
The advance search may be useful in certain instances: for example, you may want to limit your search to subject headings or other field. For example, searching "Rome" in the subject field, and "grain" anywhere, produces a much tighter search than simply entering <Rome AND Grain>.
It's also possible to click on "browse search" and browse titles, authors, or subject heading strings.
NUcat, Northwestern University Library's more traditional catalog, can also be used to find books, documents, video, sound recordings, and other items across both the Evanston and Chicago campus libraries of Northwestern University. NUcat will be available through the 2014/2015 academic year.
Sample keyword searches:
rome and trade
rome and "grain trade"
or if you want to get really sophisticated: (rome or "roman empire") and "grain trade"
Some searches (such as rome and trade) may best be done using the Guided Search and limiting to subject headings.
Sample subject Heading searches: