Time is what a clock reads. In classical, non-relativistic physics it is a scalar quantity and, like length, mass, and charge, is usually ascribed as a fundamental quantity. Mathematically, time is combined with other physical quantities to derive concepts such as motion, kinetic energy and time-dependent fields.
Around 1602, Galileo Galilei studied pendulums and discovered isochronism, the key property that makes pendulums useful to timekeepers. He found that the period of swing of a pendulum is approximately the same for differently sized swings. From his findings, Galileo in 1637 had the idea for the construction of a pendulum clock, which was partly constructed by his son in 1649, but neither lived to finish it.
The above is a drawing is probably the first design for a pendulum clock designed by Galileo around 1641. Part of the front supporting plate is removed by the artist to show the wheelwork. Although the source says the drawing is by Galileo, it is undoubtedly the one drawn by his student Vincenzo Viviani in 1659, since Galileo was blind by the time he had the idea.
This pendulum clock was partly constructed by his son Vincenzo Galilei, the illegitimate son of Galileo Galilei and his mistress Marina Gamba in 1649 who was later legitimated by his father in 1619, but neither lived to finish it.
In 1656, the Dutch scientist and inventor Christiaan Huygens, inspired by the investigations of pendulums by Galileo invented the pendulum clock. He patented his clock on June 16, 1657.