The Interurban Building, formerly known as the Seattle National Bank Building (1890–1899), the Pacific Block (1899–1930) and the Smith Tower Annex (1930–1977), is a historic office building located at Yesler Way and Occidental Way S in the Pioneer Square neighborhood of Seattle, Washington, United States. Built from 1890 to 1891 for the then recently formed Seattle National Bank, it is one of the finest examples of Richardsonian Romanesque architecture in the Pacific Northwest and has been cited by local architects as one of the most beautiful buildings in downtown Seattle. It was the breakthrough project of young architect John Parkinson, who would go on to design many notable buildings in the Los Angeles area in the late 19th and early 20th century.

The Seattle National Bank would vacate the building after only five years, followed by numerous legal battles between its owners, creditors and builders that ultimately led to the foreclosure of the building. It came under the ownership of New York industrialist Lyman Cornelius Smith who would rename it the Pacific Block in 1899. From 1904 to 1928, the Puget Sound Electric Railway's Seattle–Tacoma interurban line terminated in front of the building and the former bank lobby was used as a ticket office and waiting room. The building was threatened with demolition several times in the 1910s and 1920s but plans to replace the building with a skyscraper always fell, though. The building underwent a major interior modernization beginning in 1929 under L.C. Smith's heirs, which included demolition of the entire Southeast wing of the building. The building was renamed again to the Smith Tower Annex, which it would remain until its most recent restoration in the late 1970s after which it was renamed the Interurban Building as a nod to its role in local transportation. It was listed on the National Register of Historic Places in 1970 as a contributing property to the Pioneer Square Historic District.

The site of the Interurban Building as well as most of Pioneer Square was once part of the 1852 donation land claim of Henry Yesler and as the city grew he would gradually sell off or lease lots to prospective settlers as he needed the funds. By the late 1880s the lots at what was then the Southeast corner of Mill Street and Second Avenue South, still owned by Yesler, were covered by a collection of wooden shacks and lodging houses, the earliest dating back to the late 1860s. Among these early hostelries and adjoining several Chinese laundrys was the Wisconsin House, located over the Star Saloon where it is said that anti-Chinese sentiment that culminated in the Seattle riot of 1886 began.

In February 1889 Yesler sold the 2 lots to a group of investors consisting of J.M. Thompson, Fred E. Sander and George M. Boman, all three of which were involved with real estate development as well as having stakes in the Lake Washington Cable Railway Company. The sale price was $85,000 in a deal that would have the buyers paying $75,000 up front and the remainder on January 1, 1890, with the shrewd Yesler insisting on holding onto the property in the interim to continue collecting valuable rent on the tenants and thus delaying the buyers' intentions of building a large brick building on the site. Yesler would use the proceeds from this sale to fund the further construction of his Pioneer Block which had just broken ground. 4 months after the sale the Great Seattle Fire would clear the property and after a brief occupation by tents housing the burned-out businesses, the subsequent regrading in early 1890 would raise the streets around the property 18 feet above the original grade, leaving a dangerous hole in the ground that would claim at least one life.

The Seattle National Bank was incorporated in February 1889 with George W. E. Griffith as president, William Rankin Ballard as vice-president and Fred Warde as cashier. Griffith was a prominent banker and mortgage broker in Lawrence, Kansas and would remain there, with Ballard, then the manager of the West Coast Improvement Company and the namesake of the recently established city of Ballard, serving as acting manager. The bank opened one year later in temporary quarters on Yesler Way in the Sanderson Block (The current location of the Merchant's Cafe) with plans to locate in the Burke Building at Second Avenue and Marion Street upon its completion. The bank soon decided to have their own building built instead, with several shareholders headed by Ballard and Luther H. Griffith (no-relation to the bank president) forming the Seattle National Bank Building Company in April 1890 in order to keep the bank's finances separate from the building. It also allowed them to issue bonds to Griffith's own firm, the Western Farm Mortgage Trust Company, that they would pay back with interest for the building's construction without causing a conflict of interest. During this time they purchased the lot for their new building from Fred E. Sander, who still held an option on the now vacant property and had put it up for sale that February advertising it as the finest business lot in the city. The same month the building company was formed they solicited for designs for a proposed 6-story building of brick, iron and stone, receiving plans from a dozen different architects. They ultimately chose the plans of then 28 year old John B. Parkinson, a relative newcomer to Seattle, who had recently dissolved his partnership with Cecil Evers with whom he had designed the Butler and Epler Blocks. The proposed bank and office building was estimated to cost about $200,000, the equivalent of nearly $6 million today.

Construction of the massive foundation, said to be one of the largest being built in the city at the time, began in June 1890 with the driving of piles, with large shipments of Chuckanut Sandstone arriving by barge from the Roth & Roeder quarry in Bellingham the following month. Early reports indicated that the building's lower floors were to be faced in Tenino bluestone but this was ultimately only used for the pier bases on the ground floor. The rest of the first and second floors were to be trimmed with red Colorado sandstone from the Kenmuir quarry near Colorado Springs, the site of which is now part of the Red Rock Canyon Open Space. The use of the stone was a novelty in Seattle at the time as local grey stone was so abundant and it would guarantee that the new building would stand out amongst its peers. The remainder of the street-facing façade was to be clad in high quality pressed brick from California and trimmed with red terracotta that would match the hue of the stone, giving the building a mostly monochromatic appearance. While most of the common brick and structural lumber used in the building was from Seattle,

many of its interior finishes and hardware were sourced from across the country; Smith & Wyman of Minneapolis supplied the doors, blinds, sashes and interior moldings. Matthew Dow was awarded the general construction contract, the first of many buildings he would help build in Seattle, and by September, the walls were up to the second story.

Though completion of the building was still several months out in February 1891, the banking room, said to be the largest yet opened in Seattle, was made separately waterproof and the bank opened there that month, followed by the neighboring Seattle Savings Bank (later the Nickle then Washington Savings Bank) that June, which was connected to the National bank through common shareholders. The unfinished building was already being praised as one of the most magnificent bank buildings on the coast and would make appearances in many Architectural trade journals. A detailed description of the banking room was published in the Seattle Post-Intelligencer shortly before the bank's opening: