The Willow Grove Plank Road isn't technically in Horsham but we saw its name on a map we just discovered and figured we'd do some digging. It is now part of Easton Road running from Chestnut Hill to Willow Grove.
The following is from "Willow Grove Walking Tour" from the Upper Moreland Historical Association:
The original name ‘Roundmeadow’ was lost when in 1792 Reading Howell, a cartographer in passing through noticed a man planting willow trees. Willow trees were used by farmers to stabilize and dry out the swampy soil. Howell designated the area as Willow Grove on his map instead of Roundmeadow. The name was adopted permanently.
The large stones used in the base of York Road kept sinking deeper into their marshy beds due to weight, springs, and the thawings and freezings of winter. It has been estimated that the stone road bed is at least twenty feet thick in places (as high as a two-story house). The marshy character of the site caused an intersecting road to be laid upon planks. The ‘Plank Road’ is now known as Easton Road. According to T. Bean, “At one time the Willow Grove Swamp must have contained nearly one hundred and fifty acres. To avoid its mirey grip, Old York Road was laid out in the shape of an ‘S’. This configuration is still discernable today.(55)
and from The York Road, Old and New
he Germantown and Willow Grove Plank Road and Turnpike was laid out and made in 1856-7 and commenced on the Old York Road, a few yards above the Round Meadow bridge, crossing the Moreland and Abington lines nearly at right angles.(56)