Based on the assumption that Kentucky neutrality would act as a shield against a direct invasion from the north, circumstances that no longer applied in September 1861, Tennessee initially had sent men to Virginia and concentrated defenses in the Mississippi Valley. Even before Johnston arrived in Tennessee, construction of two forts had been started to defend the Tennessee and the Cumberland rivers, which provided avenues into the State from the north. Both forts were located in Tennessee in order to respect Kentucky neutrality, but these were not in ideal locations. Fort Henry on the Tennessee River was in an unfavorable low-lying location, commanded by hills on the Kentucky side of the river. Fort Donelson on the Cumberland River, although in a better location, had a vulnerable land side and did not have enough heavy artillery to defend against gunboats.