In general, the best way to achieve very-high pressures is to squeeze the sample with something hard.
High-Pressure Science in 55 BC
The Paris-Edinburgh cell doesn't use menhirs but works on a similar principal. The sample in placed between two hard anvils made from either tungsten-carbide or sintered industrial diamond.
Because we don't have Obelix, we use a hydraulic ram to apply the pressure.
The Paris-Edinburgh cell's hydraulic ram is a key breakthrough. It has been
very carefully designed to minimise both size and weight. The result is a
ram with a 200 tonne capacity ( enough to lift two railway locomotives) which
weighs only 50 kilogrammes and fits into a 30 cm cube.