Due to improvements in the silver and gold bullion supply and advances in minting technology, the production of both silver and gold coins increased dramatically in the 1830s. The completion of a new and much larger Philadelphia Mint building in 1833 further supported the mintage and circulation of coins. These conditions prompted Mint Director Robert Patterson to seek fresh designs and hire Christian Gobrecht to assist Chief Engraver William Kneass, who had recently suffered a debilitating stroke. Gobrecht ultimately created the Seated Liberty design employed on silver coinage of the mid to late 19th century (1836-1891), including the half dime, dime, twenty-cent piece, quarter, half dollar, and dollar denominations. Like other Seated Liberty coins, the obverse of the Seated Liberty quarter dollar features Lady Liberty seated upon a rock, holding a liberty pole and cap symbolic of freedom in her left arm and a shield in her right to defend it. The reverse design features an American Bald Eagle with outstretched wings holding an olive branch and a bundle of arrows in its talons. Production of the Seated quarter continued from 1838 until 1891, when the remaining Seated Liberty coins were replaced by the newly designed Barber series.