Howe and his brother Richard had, as part of their instructions, been assigned roles as peace commissioners, with limited authority to treat with the rebels. After Long Island, they pursued an attempt at reconciliation, sending the captured General John Sullivan to Philadelphia with a proposal for a peace conference. The meeting that resulted, conducted by Admiral Howe, was unsuccessful. The Howes had been given limited powers, as had the Congressional representatives, and the latter were insistent that the British recognise the recently declared colonial independence. This was not within the Howes' powers, so the conference failed, and Howe then continued the campaign. He first landed troops on Manhattan on 15 September and occupied New York City (which then covered only Lower Manhattan), although his advance northward on Upper Manhattan was checked the next day at Harlem Heights. He paused, spending nearly one month consolidating control of New York City and awaiting reinforcements. During this time he ordered the execution of Nathan Hale for espionage and had to deal with the effects of a major fire in the city. He then attempted a landing on the mainland at Throgs Neck, intending to flank Washington's position at Harlem Heights. However, the narrow causeway between the beach and the mainland was well-defended, and he ended up withdrawing the troops. He made a successful landing of troops at Pell's Point in Westchester County, but Washington managed to avoid being flanked, retreating to White Plains. Howe successfully forced Washington out of the New York area in the 28 October Battle of White Plains, and then turned his attention to consolidate British hold on Manhattan. In November he attacked the remaining Continental Army stronghold in the Battle of Fort Washington, taking several thousand prisoners.