You can start with a search for Boston, or the name of an architect, (Saint-Gaudens.) You can also find additional information by selecting the "Related Content" tab.
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The most authoritative encyclopedia for Architecture is the Grove Art Online, (now available through Oxford Art Online)
Most articles have an informative outline which can be useful in placing your topic in a larger context or to focus on specific time periods or issues.
You can also search within articles
Consider the bibliographies located at the end of most articles. The references are listed chronologically and allow you to trace the path of scholarship. Check for more recent and related articles and books, written by the author(s) of the encyclopedia entries and cited in the bibliographies.