The answer is: 40 years

1 Kings 11:42 - Solomon's reign lasted a remarkable 40 years, a period marked by monumental building projects, including the First Temple in Jerusalem. Interestingly, his reign aligns with Israel's peak in wealth and influence, echoing God's promise of prosperity found in Deuteronomy 28 for obedience to His commands.

Solomon’s reign was indeed an extraordinary chapter in Israel’s history, lasting 40 years — a number that echoes throughout the Bible as one of significance, representing completeness or fulfillment. Think about how the Israelites wandered in the desert for 40 years before entering the Promised Land. This theme of 40 shows up elsewhere too — Jesus fasted for 40 days, setting a period for reflection and preparation before starting His ministry.

During Solomon’s time, Israel thrived in its cultural and military power, which was not just the result of the king’s ambitions but also a reflection of a collective time of peace. The keen whispers of prosperity can be traced back to a land flowing with milk and honey, like the visions from early wilderness journeys, making Solomon’s palace not just a home but a beacon of a unified and prosperous nation.

His monumental project, the Temple, was more than a building; it became the spiritual heart of Israel. Built from the finest materials and adorned with intricate artistry, it signified Israel's relationship with the divine. Interestingly, the craftsmanship behind the Temple resonated with the skills of laborers who were either liberated Israelites or diverse people pooled from Solomon’s vast realm, showcasing the unity of various cultures under Solomon’s enlightened rule.

You could say, even today, the echoes of Solomon's reign remind us about leadership based on wisdom, which many leaders through history could still learn from as they work to build lasting legacies.