Joe bought a nice house with a yard in southern New Hampshire, ready to enjoy a quiet suburban life. A stone wall ran along the boundary line between his yard and the neighbors'. At least, that's what he thought. The wall really wasn't on the legal line. According to the true legal line, he owned about 871 square feet on the other side of the wall. This is a New Hampshire Case. However, a majority of US jurisdictions follow the law applied in this case. Unhappy with the discovery, Joe tore down the wall, claiming the additional triangle of land in his deed. Neighbor Dave was furious. Dave and the previous owners had mowed the lawn and planted a garden all the way over to the stone wall, believing it to be the boundary line as long as anyone could remember, well over 20 years. Enter the legal theory of adverse possession, which can allow folks who are not legal owners of land to gain ownership if they meet certain requirements. Adverse possessors must prove that their land use was open, continuous, exclusive, adverse and with notice to the legal owner for 20 years. The adverse aspect amounts to a trespass against the true owner. It doesn't matter if the folks claiming adverse possession only recently purchased. They can tack on the adverse use of those who owned the property before them. Someone had mistakenly built the wall inside Joe's property line decades earlier, short changing the owners of the lot of 871 square feet. The mistake was the twist in this case. At first, the trial court held that Joe shouldn't loose the land because there could be no notice or adversity to the people who sold the lot where there was a mistaken belief over where the true line was. But that ruling was appealed. The appellate court found that it makes no difference that the parties were mistaken. Subjective personal beliefs make no difference and did not in any way stop the adversely possessed parties' ability to gain notice of the wrongful possession. In Mastroianni v. Wercinski, decided in February, 2009, the New Hampshire Supreme Court held that where a non owner of land shows signs of using that land under the mistaken belief that they are holding up to the true legal line, they actually gain legal ownership up to that line, regardless of the mistake. Note that in this case there was a clear and certain boundary, a stone wall. Other cases all over the country involved mistakenly built wooden fences, driveways, and a Massachusetts case where a railroad spike designated the end of a triangle. Robert Frost wrote that "good fences make good neighbors." But, in this case the decades old stone wall made for ill will and a court imposed relocation of the boundary line under the centuries old law of adverse possession. Again, this is a New Hampshire Case. But, a majority of US states follow the law as applied in this case.