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.
Books are all assigned subject terms from a standard vocabulary call Library of Congress Subject headings. Using these standard subject terms is one way to find materials that might not be found by the keywords you have in mind. These subject terms are always listed when you display the full record for the book in NUSearch :
To make use of subject headings, you may:
Sample subject Heading searches: