Under the name of megalithic monuments we include _tumuli, dolmens, cromlechs, menhirs_, and _covered avenues_. It may at first sight appear strange to include tumuli amongst stone monuments, but they almost always enclose a dolmen, a cist, or a crypt communicating with the outside by a covered passage. The excavation of more than four hundred tumuli in England has brought to light now, a stone coffer made of a number of stones set edgeways and called a _kistvaen_: now of a, tomb hollowed out beneath the surface of the ground, and enclosed by huge blocks of stone.1 Mounds are as numerous in Portugal as tumuli in England, and the fact that they are of low height has led to their being called _mamoas_ or _maminhas_, which signifies little mounds. In Poland, tumuli consist of piles of massive stones; beneath each is a cist made of four large slabs, and containing as many as eight or ten urns full of calcined bones. The excavation of a tumulus in the plain of Tarbes brought to light an enormous block of granite resting on blocks of quartz. The spaces between these blocks were filled in with rubble made of small stones cemented into one mass with clay. Edwin-Harness Mound, near Liberty (Ohio), is 160 feet long by eighty or ninety wide, and thirteen to eighteen high in the middle. It contained a dozen sepulchral chambers. [Illustration: 56.] The large dolmen of Coreoro, near Plouharnel. More rarely tumuli are merely artificial mounds of earth, sometimes rising to a great height. Those of North America are the most remarkable known. That of Cahokia is now ninety-one feet high,2 and was formerly surmounted by a low pyramid, now destroyed. Its base measures 560 feet by 720, the platform at the top is 146 feet by 310 feet wide, and it has been estimated that twenty-five million cubic feet of earth were used in its construction. Major Pearse mentions a tumulus near Nagpore, which is 3,900 feet in circumference, and 174 feet high. Another between Tyre and Sarepta, is 130 feet high by 650 in diameter. It has never been excavated.3 [Illustration: 57.] Dolmen of Arrayolos (Portugal). The dolmen type of monument is a rectangle of u hewn upright stones covered over with a slab laid across them; this slab being the largest block of stone that could be found in the neighborhood or obtained by the builders.