What is arguably the most frightful episode of Nazi mass murder took place in four camps on Polish soil that were exclusively built for and dedicated to the systematic killing of human beings – a phenomenon without precedent in human history. According to the most recent data available, these four camps accounted for at least 1,551,000 deaths. All known evidence indicates that much of the remains of these camps' victims still lie under the ground once occupied by these camps, especially in what is left of the huge pits that were used to bury the corpses of those murdered before it was decided to cremate them.
This chapter starts with a presentation of what is known about the mass graves at these four camps, mainly from forensic and archaeological investigations, followed by a discussion of the main claims and arguments adduced by Holocaust deniers (so-called Revisionists) Carlo Mattogno, Jürgen Graf, and Thomas Kues, whereby the physical evidence of said mass graves is not compatible with or need not correspond to mass murder on the scale that historiography has established. The focus will be the camps of the killing operation known as Aktion Reinhard, Belzec, Sobibor and Treblinka, which are the subject of a trilogy authored by the mentioned Revisionist trio or one or more of its members. The mass graves at Chelmno extermination camp, and Mattogno’s related claims in his book about Chelmno, have been discussed in a blog article which will be briefly summarized in this chapter.
 Bełżec: 434,508 deportees (rounded to 435,000) mentioned in the Höfle telegram, cf. Witte and Tyas, ‘A New Diocument’. Sobibór: 170,165 (rounded to 170,000), thereof 101,370 until 31 December 1942 mentioned in the Höfle Report plus 68,795 in 1943, see Schelvis 2007, p. 198. Treblinka: 713,555 until 31 December 1942 mentioned in the Höfle telegram, plus 8,000 deportees from Theresienstadt in October 1942, mentioned in Arad, ‘Reinhard’, pp. 141-142, which the author assumes not to be included in Höfle’s figure. In 1943 there arrived a recorded 53,149 deportees from the General Government and the Bialystok District (including 2,000 Sinti and Roma) and 14,159 deportees from Saloniki, Macedonia and Thessaloniki (Młynarczyk, Treblinka, pp. 280-1.) The total number of recorded deportees to Treblinka was thus 788,863 (rounded to 789,000). Chełmno: About 145,000 Jews and 5,000 Gypsies in the camp’s 1st phase (December 1941 to March 1943), more than 7,000 Jews in the second phase (23 June to 14 July 1944), see the Bonn Court of Assizes’ (LG Bonn) judgment of 30.3.1963 against former members of the Chełmno staff, published in JuNSV Band XXI, quoted in Rückerl, ‘Vernichtungslager’, pp. 252 – 295. Where these figures differ from those in chapter 3, they should be seen as minimum figures.
 Mattogno, Bełżec, MGK, Sobibór and M&G, Treblinka. Where there is also a version in another language, references are made to the respective English version, unless otherwise stated.
 Carlo Mattogno, Chelmno, 2009.
 Roberto Muehlenkamp, ‘Mattogno on Chełmno Mass Graves’, Holocaust Controversies, http://holocaustcontroversies.blogspot.com/2010/12/mattogno-on-chemno-mass-graves.html