The microstructures and mechanical properties of tantalum carbides containing predominantly the -Ta4C3-x phase are compared with the properties of the monocarbide (-TaC) and the hemicarbide (-Ta2C) and two-phase composites. It is shown that a Ta and -TaC powder mixture corresponding to a C/Ta at. ratio of 0.66 can be hot-pressed (1800 degrees C, 2h) to obtain similar to 95wt% of -Ta4C3-x with a density of 98% of theoretical. This material has an attractive combination of high fracture toughness (13.8 +/- 0.2MPam) and fracture strength (759 +/- 24MPa) with modest hardness (5.6 +/- 0.5GPa). The fracture toughness and strength measured for this material were the highest among all the materials with C/Ta ratio ranging from 0.5 (hemicarbide) to 1.0 (monocarbide). It is also shown that a material containing 86wt% -Ta4C3-x can be consolidated by pressureless sintering of a hydrogenated Ta and -TaC powder mixture without significant drop in density (97% of theoretical) or mechanical properties (13.4 +/- 0.2MPam, 700 +/- 20MPa, 6.0 +/- 0.4GPa). Materials containing high weight fraction of the -Ta4C3-x phase exhibited rising crack-growth-resistance (R-curve) behavior. Optical and scanning electron microscope observations suggested crack-face bridging was the dominant toughening mechanism. The crack-bridging ligaments were lamellae of the basal planes of the -Ta4C3-x phase produced by their easy cleavage. The thickness of the lamellae ranged from 40 to 2000nm, significantly less than the grain size.